System and method for determining a hitch angle offset

ABSTRACT

A system and a method are provided for estimating an actual hitch angle between a vehicle and a trailer. A hitch sensor on the vehicle continuously senses a measured hitch angle and a steering sensor continuously senses a steering angle of steered wheels of the vehicle. A controller determines an offset between the measured hitch angle and the actual hitch angle when the measured hitch angle and the steering angle are substantially constant while the vehicle and trailer are reversing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of co-pending U.S.patent application Ser. No. 14/188,213, which was filed on Feb. 24,2014, entitled “SENSOR SYSTEM AND METHOD FOR MONITORING TRAILER HITCHANGLE,” which is a continuation-in-part of U.S. patent application Ser.No. 13/847,508, which was filed on Mar. 20, 2013, entitled “HITCH ANGLEESTIMATION,” and a continuation-in-part of co-pending U.S. patentapplication Ser. No. 14/161,832, which was filed on Jan. 23, 2014,entitled “SUPPLEMENTAL VEHICLE LIGHTING SYSTEM FOR VISION BASED TARGETDETECTION,” which is a continuation-in-part of U.S. patent applicationSer. No. 14/068,387, which was filed on Oct. 31, 2013, entitled “TRAILERMONITORING SYSTEM AND METHOD,” which is a continuation-in-part of U.S.patent application Ser. No. 14/059,835, which was filed on Oct. 22,2013, entitled “TRAILER BACKUP ASSIST SYSTEM,” which is acontinuation-in-part of U.S. patent application Ser. No. 13/443,743which was filed on Apr. 10, 2012, entitled “DETECTION OF ANDCOUNTERMEASURES FOR JACKKNIFE ENABLING CONDITIONS DURING TRAILER BACKUPASSIST,” which is a continuation-in-part of U.S. patent application Ser.No. 13/336,060, which was filed on Dec. 23, 2011, entitled “TRAILER PATHCURVATURE CONTROL FOR TRAILER BACKUP ASSIST,” which claims benefit fromU.S. Provisional Patent Application No. 61/477,132, which was filed onApr. 19, 2011, entitled “TRAILER BACKUP ASSIST CURVATURE CONTROL,” whichhave a common Applicant herewith and are being incorporated herein intheir entirety by reference.

FIELD OF THE INVENTION

The disclosure made herein relates generally to driver assist and activesafety technologies in vehicles, and more particularly to a trailerbackup assist system.

BACKGROUND OF THE INVENTION

Reversing a vehicle while towing a trailer is very challenging for manydrivers. This is particularly true for drivers that are unskilled atbacking vehicles with attached trailers, which may include those thatdrive with a trailer on an infrequent basis (e.g., have rented atrailer, use a personal trailer on an infrequent basis, etc.). Onereason for such difficulty is that backing a vehicle with an attachedtrailer requires steering inputs that are opposite to normal steeringwhen backing the vehicle without a trailer attached and/or requiresbraking to stabilize the vehicle-trailer combination before a jackknifecondition occurs. Another reason for such difficulty is that smallerrors in steering while backing a vehicle with an attached trailer areamplified thereby causing the trailer to depart from a desired path.

To assist the driver in steering a vehicle with a trailer attached, atrailer backup assist system needs to know the driver's intention. Onecommon assumption with known trailer backup assist systems is that adriver of a vehicle with an attached trailer wants to backup straightand the system either implicitly or explicitly assumes a zero curvaturepath for the vehicle-trailer combination. Unfortunately most of thereal-world use cases of backing a trailer involve a curved path and,thus, assuming a path of zero curvature would significantly limitusefulness of the system. Some known systems assume that a path is knownfrom a map or path planner. To this end, some known trailer backupassist systems operate under a requirement that a trailer backup path isknown before backing of the trailer commences such as, for example, froma map or a path-planning algorithm. Undesirably, such implementations ofthe trailer backup assist systems are known to have a relatively complexhuman machine interface (HMI) device to specify the path, obstaclesand/or goal of the backup maneuver. Furthermore, such systems alsorequire some way to determine how well the desired path is beingfollowed and to know when the desired goal, or stopping point andorientation, has been met, using approaches such as cameras, inertialnavigation, or high precision global positioning system (GPS). Theserequirements lead to a relatively complex and costly system.

Another reason backing a trailer can prove to be difficult is the needto control the vehicle in a manner that limits the potential for ajackknife condition to occur. A trailer has attained a jackknifecondition when a hitch angle cannot be reduced (i.e., made less acute)while continuously backing up a trailer by application of a maximumsteering input for the vehicle such as, for example, by moving steeredfront wheels of the vehicle to a maximum steered angle at a maximum rateof steering angle change. In the case of the jackknife angle beingachieved, the vehicle must be pulled forward to relieve the hitch anglein order to eliminate the jackknife condition and, thus, allow the hitchangle to be controlled via manipulation of the steered wheels of thevehicle. However, in addition to the jackknife condition creating theinconvenient situation where the vehicle must be pulled forward, it canalso lead to damage to the vehicle and/or trailer if certain operatingconditions of the vehicle relating to its speed, engine torque,acceleration, and the like are not detected and counteracted. Forexample, if the vehicle is travelling at a suitably high speed inreverse and/or subjected to a suitably high longitudinal accelerationwhen the jackknife condition is achieved, the relative movement of thevehicle with respect to the trailer can lead to contact between thevehicle and trailer thereby damaging the trailer and/or the vehicle.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method is providedfor estimating an actual hitch angle between a vehicle and a trailer.The method includes sensing a measured hitch angle with a hitch sensoron the vehicle, sensing a steering angle of steered wheels of thevehicle, and reversing the vehicle. The method also includes determiningan offset between the measured hitch angle and the actual hitch anglewhen the measured hitch angle and the steering angle are substantiallyconstant while the vehicle is reversing.

According to another aspect of the present invention, a method isprovided for estimating an actual hitch angle between a vehicle and atrailer. The method includes sensing a measured hitch angle continuouslyand sensing a steering angle of the vehicle continuously. The methodalso includes determining an offset between the measured hitch angle andthe actual hitch angle when the measured hitch angle and the steeringangle are substantially constant while the vehicle and the trailer arereversing over a threshold distance.

According to a further aspect of the present invention, a system isprovided for estimating an actual hitch angle between a vehicle and atrailer. The system includes a hitch sensor on the vehicle continuouslysensing a measured hitch angle and a steering sensor continuouslysensing a steering angle of the vehicle. The system also includes acontroller that determines an offset between the measured hitch angleand the actual hitch angle when the measured hitch angle and thesteering angle are substantially constant while the vehicle and trailerare reversing.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a vehicle-trailer combination, the vehicle being configuredfor performing trailer backup assist functionality in accordance with anembodiment;

FIG. 2 shows one embodiment of the trailer backup steering inputapparatus discussed in reference to FIG. 1;

FIG. 3 shows an example of a trailer backup sequence implemented usingthe trailer backup steering input apparatus discussed in reference toFIG. 2;

FIG. 4 shows a method for implementing trailer backup assistfunctionality in accordance with an embodiment;

FIG. 5 is a diagrammatic view showing a kinematic model configured forproviding information utilized in providing trailer backup assistfunctionality in accordance with one embodiment;

FIG. 6 is a graph showing an example of a trailer path curvaturefunction plot for a rotary-type trailer backup steering input apparatusconfigured in accordance with the disclosed subject matter;

FIG. 7 is a diagrammatic view showing a relationship between hitch angleand steered angle as it relates to determining a jackknife angle for avehicle/trailer system in reverse or backing up;

FIG. 8 shows a method for implementing jackknife countermeasuresfunctionality in accordance with an embodiment;

FIG. 9 shows a human machine interface (HMI) device associated with thetrailer backup assist;

FIG. 10 shows a flow diagram associated with the trailer backup assist;

FIG. 11 shows a flow diagram of the setup module according to oneembodiment;

FIG. 12 shows an example of an image displayed at the HMI device inaccordance with one embodiment;

FIG. 13 is a block diagram illustrating the vehicle trailer backupassist system employing a target monitor controller, according to oneembodiment;

FIG. 14 is a schematic diagram illustrating user placement of the targeton a trailer towed by a vehicle;

FIG. 15 is an enlarged view of the front portion of the trailer furtherillustrating the target placement zone in relation to the targetsticker;

FIG. 16 is a front view of a portable device having a displayillustrating the overlay of a target onto a target placement zone on thetrailer;

FIG. 17 is a flow diagram illustrating a method of assisting a user withthe placement of the target on the trailer;

FIG. 18 is a flow diagram illustrating a method of monitoring placementof the target on the trailer and generating feedback alert;

FIG. 19 is a schematic view of a front portion of the trailer having atarget mounting system assembled thereto, according to one embodiment;

FIG. 20 is an exploded view of the target mounting system and trailershown in FIG. 19;

FIG. 21 is a flow diagram illustrating an initial set up routine formonitoring the trailer connection for target changes and resettingtrailer selection;

FIG. 22 is a flow diagram illustrating a target moved detection routinefor monitoring presence of trailer changes and resetting trailerselection;

FIG. 23A is an image of the trailer showing the target in a firstposition;

FIG. 23B is an image of the trailer showing movement of the target to asecond position, according to one example;

FIG. 24 is a flow diagram illustrating a trailer connection monitoringroutine for monitoring trailer disconnection;

FIG. 25A is an image of a tow vehicle showing a keylock hole defined ina tailgate handle assembly of the tow vehicle;

FIG. 25B is an enlarged partial rear perspective view of a tailgatehandle assembly defining a keylock hole;

FIG. 25C is an enlarged partial front perspective view of the tailgatehandle assembly showing the customary use of a keylock cylinder with thekeylock hole;

FIG. 25D shows the keylock cylinder mounted to the tailgate handle,according to one embodiment;

FIG. 26A is a front perspective view of a light assembly, according toone embodiment;

FIG. 26B is a rear perspective view of the light assembly;

FIG. 26C is an exploded view of the light assembly shown in FIGS. 26Aand 26B;

FIG. 26D is a cross sectional view of the light assembly taken alongline XXVI D-XXVI D of FIG. 26A;

FIG. 27A is a light assembly mounted to the tailgate handle assemblyshown in FIG. 25B, according to one embodiment;

FIG. 27B is an enlarged partial front perspective view of the tailgatehandle assembly equipped with the light assembly shown in FIG. 27A;

FIG. 28 is a schematic diagram illustrating a supplemental vehiclelighting system being implemented in the tow vehicle shown in FIG. 25A,wherein the tow vehicle is attached to a trailer and features a trailerbackup assist system employing vision based target detection;

FIG. 29 is a top plan view of a trailer attached to a vehicle having asensor system, according to one embodiment;

FIG. 30 is a block diagram illustrating the trailer backup assist systememploying a sensor system that has a primary sensor and a secondarysensor, according to one embodiment;

FIG. 31 is a flow diagram illustrating a method for estimating an actualhitch angle of a trailer attached to a vehicle with a sensor system;

FIG. 32 is an automotive vehicle having a hitch angle estimating systemof the disclosed subject matter;

FIG. 33 is a block diagram of a vehicle having a trailer coupled theretoand a relationship to the law of cosines;

FIG. 34 is a flow chart of a method of estimating a hitch angle;

FIG. 35 is a block diagram illustrating one embodiment of the trailerbackup assist system having the trailer backup assist control modulewith a hitch angle calibration routine;

FIG. 36 is a diagram that illustrates the geometry of a vehicle and atrailer overlaid with a two-dimensional x-y coordinate system thatidentifies variables used to calculate kinematic information of thevehicle and trailer system;

FIG. 37 is a flow diagram illustrating one embodiment of the hitch anglecalibration routine;

FIG. 38 is a flow diagram illustrating an initiating routine that ispreformed prior to calculating the trailer angle offset, according toone embodiment;

FIG. 39 is a flow diagram illustrating an additional embodiment of thehitch angle calibration routine;

FIG. 40 is a flow diagram illustrating a method of calibrating a trailerbackup assist system before determining an offset of the measured hitchangle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While various aspects of the inventive subject matter are described withreference to a particular illustrative embodiment, the inventive subjectmatter is not limited to such embodiments, and additional modifications,applications, and embodiments may be implemented without departing fromthe inventive subject matter. In the figures, like reference numberswill be used to illustrate the same components. Those skilled in the artwill recognize that the various components set forth herein may bealtered without varying from the scope of the inventive subject matter.

The disclosed subject matter is directed to providing trailer backupassist functionality in a manner that is relatively low cost and thatoffers an intuitive user interface. In particular, such trailer backupassist functionality provides for controlling curvature of a path oftravel of a trailer attached to a vehicle (i.e., trailer path curvaturecontrol) by allowing a driver of the vehicle to specify a desired pathof the trailer by inputting a desired trailer path curvature as thebackup maneuver of the vehicle and trailer progresses. Although acontrol knob, a set of virtual buttons, or a touch screen can each beimplemented for enabling trailer path curvature control, the disclosedsubject matter is not unnecessarily limited to any particularconfiguration of interface through which a desired trailer pathcurvature is inputted. Furthermore, in the case where a steering wheelcan be mechanically decoupled from steered wheels of the vehicle, thesteering wheel can also be used as an interface through which a desiredtrailer path curvature is inputted. As will be discussed herein ingreater detail, kinematical information of a system defined by thevehicle and the trailer are used to calculate a relationship (i.e.,kinematics) between the trailer's curvature and the steering angle ofthe vehicle for determining steering angle changes of the vehicle forachieving the specified trailer path. Steering commands corresponding tothe steering angle changes are used for controlling a steering system ofthe tow vehicle (e.g., electric power assisted steering (EPAS) system)for implementing steering angle changes of steered wheels of the vehicleto achieve (e.g., to approximate) the specified path of travel of thetrailer. The trailer backup assist system automatically steers thevehicle-trailer combination as a driver uses the vehicle transmission,accelerator and brake to reverse the vehicle-trailer combination. Thedriver inputs a desired trailer curvature command by using an inputdevice such as a trailer steering knob.

Trailer backup assist functionality may be directed to implementing oneor more countermeasures for limiting the potential of a jackknifecondition being attained between a vehicle and a trailer being towed bythe vehicle while backing up. In certain embodiments, curvature of apath of travel of the trailer (i.e., trailer path curvature control) canbe controlled by allowing a driver of the vehicle to specify a desiredpath of the trailer by inputting a desired trailer path curvature as thebackup maneuver of the vehicle and trailer progresses. Although acontrol knob, a set of virtual buttons, or a touch screen can each beimplemented for enabling trailer path curvature control, the disclosedsubject matter is not unnecessarily limited to any particularconfiguration of interface through which a desired trailer pathcurvature is inputted. Furthermore, in the case where a steering wheelcan be mechanically decoupled from steered wheels of the vehicle, thesteering wheel can also be used as an interface through which a desiredtrailer path curvature is inputted. As will be discussed herein ingreater detail, kinematic information of a system defined by the vehicleand the trailer are used to calculate a relationship (i.e., kinematics)between the trailer's curvature and the steering angle of the vehiclefor determining steering angle changes of the vehicle for achieving thespecified trailer path. Steering commands corresponding to the steeringangle changes are used for controlling a steering system of the towvehicle (e.g., electric power assisted steering (EPAS) system) forimplementing steering angle changes of steered wheels of the vehicle toachieve (e.g., to approximate) the specified path of travel of thetrailer.

Embodiments of the disclosed subject matter are directed to trailerbackup assist functionality that provides for a user interface for asystem that controls curvature of a path of a trailer being backed by avehicle. More specifically, trailer backup assist functionalityconfigured in accordance with embodiments of the disclosed subjectmatter provide for such trailer path curvature control by allowing adriver of the vehicle to specify a desired path of the trailer byinputting a desired trailer path curvature as the backup maneuver of thevehicle and trailer progresses. In response to such path of the trailerbeing specified by the driver, embodiments of the disclosed subjectmatter control a power assisted steering system (e.g., electric powerassisted steering (EPAS) system) of the vehicle for implementingsteering angle changes of steered wheels of the vehicle to achieve thespecified trailer path. Kinematics of the vehicle and the trailer areused to determine the steering angle changes that are required forachieving the specified trailer path. Accordingly, embodiments of thedisclosed subject matter provide for implementation of trailer backupassist functionality in a manner that is relatively simple and thatenables use of an intuitive vehicle operator interface for specifyingtrailer path curvature control.

The disclosed subject matter, furthermore, includes embodiments directedto determining a hitch angle of trailer attached to the vehicle. In onesuch embodiment, the vehicle trailer backup assist system may utilize atarget placed on the trailer, allowing the trailer backup assist systemto employ information acquired via image acquisition and processing ofthe target. According to other embodiments, the target may be used toidentify if a connected trailer has changed, trailer connection ordisconnection, and other trailer related information. The target is anidentifiable visual target that can be captured in an image by the videoimaging camera and detected and processed via image processing.According to one embodiment, the target may attached to the trailer,preferably within a target placement zone, such that the camera andimage processing may detect the target and its location on the trailerto determine trailer related information, such as the hitch anglebetween the trailer and the towing vehicle. The trailer backup assistsystem may provide to the user one or more image(s) of the trailertarget zone for proper placement of the target to assist with placementof the target on the trailer. Additionally, the vehicle trailer backupassist system may monitor the target to determine if the target has beencorrectly placed within a desired target placement zone and providefeedback alert(s) to the user. Further, the trailer backup assist systemmay monitor the trailer connection by monitoring the target to determineif the target has moved to determine whether the same trailer remainsconnected to the tow vehicle, and may initiate action in responsethereto. Further, the trailer backup assist system may monitor the hitchangle or the target to determine if the trailer may have been changedout (i.e., disconnected and replaced with another trailer), and mayinitiate action in response thereto.

The disclosed subject matter also provides a supplemental vehiclelighting system that is responsive to a trailer backup assist system.The system includes a rear vehicle fixture defining a keylock holecustomarily used in conjunction with a corresponding keylock cylinder. Alight assembly is provided in the place of a keylock cylinder andoperably coupled to the keylock hole. The light assembly includes ahousing having a barrel that is concentrically aligned with the keylockhole and includes a distal end and a proximal end. A lighting device isdisposed inside the housing and operable to emit light through thebarrel beginning from the proximal end. A lens is coupled to the distalend of the barrel and is disposed to at least partially coincide withthe keylock hole, wherein the lens is configured to disperse lightemitted from the lighting device to illuminate a rear vehicle area.

In some embodiments of the disclosed trailer backup assist system, itcan be advantageous to use information that is representative of a hitchangle between the vehicle and a trailer attached to the vehicle. Thedisclosed subject matter provides embodiments directed to estimating anactual hitch angle of a trailer attached to a vehicle, as in somesituations sensor information may become unavailable or may otherwisenot provide an accurate measurement of the hitch angle. A hitch anglethat is not accurate may introduce a potential for inadequate orimproper vehicle system control, especially when the hitch angleinformation is important to controlling the vehicle system, such as atrailer backup assist system or a trailer brake controller. According toone embodiment, a sensor system for estimating an actual hitch angle ofa trailer attached to a vehicle includes a primary sensor having acamera monitoring a target on the trailer to determine a measured hitchangle and a secondary sensor that monitors the trailer to determine anindicator of the actual hitch angle. The trailer backup assist systemmay then operate the vehicle when the measured hitch angle correlateswith the indicator of the actual hitch angle, confirming that themeasured hitch angle is a generally accurate estimate of the actualhitch angle.

According to an additional embodiment of the disclosed subject matter, asystem for estimating a hitch angle between a vehicle and a trailercoupled thereto has a wireless receiver on the vehicle located apredetermined distance from a trailer mount and a wireless transmitterlocated at an end of the trailer opposite the trailer mount. Accordingto one embodiment, a controller monitors power returns of a signaltransmitted from the transmitter to the receiver and thereby estimates adistance between the transmitter and the receiver as a function of apath loss propagation of the transmitted signal. The hitch angle is thenestimated using the estimated distance, the predetermined distance, anda trailer length.

To further ensure the accuracy of the measured hitch angle, inadditional embodiments the trailer back assist system may include ahitch angle calibration routine for determining any offset between themeasured hitch angle and the actual hitch angle, based on certainvehicle and/or trailer characteristics. In one of these embodiments, amethod provides for sensing a measured hitch angle with at least onehitch angle sensor on the vehicle and sensing a steering angle of thesteered wheels of the vehicle. The method further provides for reversingthe vehicle, and thereby determining an offset between the measuredhitch angle and the actual hitch angle when the measured hitch angle andthe steering angle are substantially consistent while the vehicle isreversing. Another one of these embodiments provides driving the vehicleforward substantially straight above a threshold speed while sensing ayaw rate of the vehicle and sensing a measured hitch angle of thetrailer. Further, the method provides for determining an angle ratebased on the measured hitch angle, and then determining an offsetbetween the measured hitch angle and the actual hitch angle when the yawrate and the angle rate are substantially zero. The offset may then beused to more accurately manipulate the actual hitch angle with thetrailer backup assist system.

Trailer Backup Assist System

Referring to FIG. 1, an embodiment of a vehicle 100 configured forperforming trailer backup assist functionality is shown. A trailerbackup assist system 105 of the vehicle 100 controls the curvature ofpath of travel of a trailer 110 that is attached to the vehicle 100.Such control is accomplished through interaction of a power assistedsteering system 115 of the vehicle 100 and the trailer backup assistsystem 105. During operation of the trailer backup assist system 105while the vehicle 100 is being reversed, a driver of the vehicle 100 issometimes limited in the manner in which he/she can make steering inputsvia a steering wheel of the vehicle 100. This is because in certainvehicles the trailer backup assist system 105 is in control of the powerassisted steering system 115 and the power assisted steering system 115is directly coupled to the steering wheel (i.e., the steering wheel ofthe vehicle 100 moves in concert with steered wheels of the vehicle100). As is discussed below in greater detail, a human machine interface(HMI) device of the backup assist system 105 is used for commandingchanges in curvature of a path of the trailer 110 such as a knob,thereby decoupling such commands from being made at the steering wheelof the vehicle 100. However, some vehicles configured to provide trailerbackup assist functionality in accordance with the disclosed subjectmatter will have the capability to selectively decouple steeringmovement from movement of steerable wheels of the vehicle, therebyallowing the steering wheel to be used for commanding changes incurvature of a path of a trailer during such trailer backup assist.

The trailer backup assist system 105 includes a trailer backup assistcontrol module 120, a trailer backup steering input apparatus 125, and ahitch angle detection apparatus 130. The trailer backup assist controlmodule 120 is connected to the trailer backup steering input apparatus125 and the hitch angle detection apparatus 130 for allowingcommunication of information therebetween. It is disclosed herein thatthe trailer backup steering input apparatus can be coupled to thetrailer backup assist control module 120 in a wired or wireless manner.The trailer backup assist system control module 120 is attached to apower steering assist control module 135 of the power steering assistsystem 115 for allowing information to be communicated therebetween. Asteering angle detection apparatus 140 of the power steering assistsystem 115 is connected to the power steering assist control module 135for providing information thereto. The trailer backup assist system isalso attached to a brake system control module 145 and a powertraincontrol module 150 for allowing communication of informationtherebetween. Jointly, the trailer backup assist system 105, the powersteering assist system 115, the brake system control module 145, thepowertrain control module 150, and the gear selection device (PRNDL),define a trailer backup assist architecture configured in accordancewith an embodiment.

The trailer backup assist control module 120 is configured forimplementing logic (i.e., instructions) for receiving information fromthe trailer backup steering input apparatus 125, the hitch angledetection apparatus 130, the power steering assist control module 135,the brake system control module 145, and the powertrain control module150. The trailer backup assist control module 120 (e.g., a trailercurvature algorithm thereof) generates vehicle steering information as afunction of all or a portion of the information received from thetrailer backup steering input apparatus 125, the hitch angle detectionapparatus 130, the power steering assist control module 135, the brakesystem control module 145, and the powertrain control module 150.Thereafter, the vehicle steering information is provided to the powersteering assist control module 135 for affecting steering of the vehicle100 by the power steering assist system 115 to achieve a commanded pathof travel for the trailer 110.

The trailer backup steering input apparatus 125 provides the trailerbackup assist control module 120 with information defining the commandedpath of travel of the trailer 110 to the trailer backup assist controlmodule 120 (i.e., trailer steering information). The trailer steeringinformation can include information relating to a commanded change inthe path of travel (e.g., a change in radius of path curvature) andinformation relating to an indication that the trailer is to travelalong a path defined by a longitudinal centerline axis of the trailer(i.e., along a substantially straight path of travel). As will bediscussed below in detail, the trailer backup steering input apparatus125 preferably includes a rotational control input device for allowing adriver of the vehicle 100 to interface with the trailer backup steeringinput apparatus 125 to command desired trailer steering actions (e.g.,commanding a desired change in radius of the path of travel of thetrailer and/or commanding that the trailer travel along a substantiallystraight path of travel as defined by a longitudinal centerline axis ofthe trailer). In a preferred embodiment, the rotational control inputdevice is a knob rotatable about a rotational axis extending through atop surface/face of the knob. In other embodiments, the rotationalcontrol input device is a knob rotatable about a rotational axisextending substantially parallel to a top surface/face of the knob.

Some vehicles (e.g., those with active front steer) have a powersteering assist system configuration that allows a steering wheel to bepartially decoupled from movement of the steered wheels of such avehicle. Accordingly, the steering wheel can be rotated independent ofthe manner in which the power steering assist system of the vehiclecontrols the steered wheels (e.g., as commanded by vehicle steeringinformation provided by a power steering assist system control modulefrom a trailer backup assist system control module configured inaccordance with one embodiment). As such, in these types of vehicleswhere the steering wheel can be selectively decoupled from the steeredwheels to allow independent operation thereof, trailer steeringinformation of a trailer backup assist system configured in accordancewith the disclosed subject matter can be provided through rotation ofthe steering wheel. Accordingly, it is disclosed herein that in certainembodiments, the steering wheel is an embodiment of a rotational controlinput device in the context of the disclosed subject matter. In suchembodiments, the steering wheel would be biased (e.g., by an apparatusthat is selectively engageable/activatable) to an at-rest positionbetween opposing rotational ranges of motion.

The hitch angle detection apparatus 130, which operates in conjunctionwith a hitch angle detection component 155 of the trailer 110, providesthe trailer backup assist control module 120 with information relatingto an angle between the vehicle 100 and the trailer 110 (i.e., hitchangle information). In a preferred embodiment, the hitch angle detectionapparatus 130 is a camera-based apparatus such as, for example, anexisting rear view camera of the vehicle 100 that images (i.e., visuallymonitors) a target (i.e., the hitch angle detection component 155)attached the trailer 110 as the trailer 110 is being backed by thevehicle 100. Preferably, but not necessarily, the hitch angle detectioncomponent 155 is a dedicated component (e.g., an item attachedto/integral with a surface of the trailer 110 for the express purpose ofbeing recognized by the hitch angle detection apparatus 130).Alternatively, the hitch angle detection apparatus 130 can be a devicethat is physically mounted on a hitch component of the vehicle 100and/or a mating hitch component of the trailer 110 for determining anangle between centerline longitudinal axes of the vehicle 100 and thetrailer 110. The hitch angle detection apparatus 130 can be configuredfor detecting a jackknife enabling condition and/or related information(e.g., when a hitch angle threshold has been met).

The power steering assist control module 135 provides the trailer backupassist control module 120 with information relating to a rotationalposition (e.g., angle) of the steering wheel angle and/or a rotationalposition (e.g., turning angle(s)) of steered wheels of the vehicle 100.In certain embodiments, the trailer backup assist control module 120 canbe an integrated component of the power steering assist system 115. Forexample, the power steering assist control module 135 can include atrailer backup assist algorithm for generating vehicle steeringinformation as a function of all or a portion of information receivedfrom the trailer backup steering input apparatus 125, the hitch angledetection apparatus 130, the power steering assist control module 135,the brake system control module 145, and the powertrain control module150.

The brake system control module 145 provides the trailer backup assistcontrol module 120 with information relating to vehicle speed. Suchvehicle speed information can be determined from individual wheel speedsas monitored by the brake system control module 145 or may be providedby an engine control module with signal plausibility. Vehicle speed mayalso be determined from an engine control module. In some instances,individual wheel speeds can also be used to determine a vehicle yaw rateand such yaw rate can be provided to the trailer backup assist controlmodule 120 for use in determining the vehicle steering information. Incertain embodiments, the trailer backup assist control module 120 canprovide vehicle braking information to the brake system control module145 for allowing the trailer backup assist control module 120 to controlbraking of the vehicle 100 during backing of the trailer 110. Forexample, using the trailer backup assist control module 120 to regulatespeed of the vehicle 100 during backing of the trailer 110 can reducethe potential for unacceptable trailer backup conditions. Examples ofunacceptable trailer backup conditions include, but are not limited to,a vehicle over speed condition, a high hitch angle rate, trailer angledynamic instability, a calculated theoretical trailer jackknifecondition (defined by a maximum vehicle steering angle, drawbar length,tow vehicle wheelbase and an effective trailer length), or physicalcontact jackknife limitation (defined by an angular displacement limitrelative to the vehicle 100 and the trailer 110), and the like. It isdisclosed herein that the backup assist control module 120 can issue asignal corresponding to a notification (e.g., a warning) of an actual,impending, and/or anticipated unacceptable trailer backup condition.

The powertrain control module 150 interacts with the trailer backupassist control module 120 for regulating speed and acceleration of thevehicle 100 during backing of the trailer 110. As mentioned above,regulation of the speed of the vehicle 100 is necessary to limit thepotential for unacceptable trailer backup conditions such as, forexample, jackknifing and trailer angle dynamic instability. Similar tohigh-speed considerations as they relate to unacceptable trailer backupconditions, high acceleration and high dynamic driver curvature requestscan also lead to such unacceptable trailer backup conditions.

Steering Input Apparatus

Referring now to FIG. 2, an embodiment of the trailer backup steeringinput apparatus 125 discussed in reference to FIG. 1 is shown. Arotatable control element in the form of a knob 170 is coupled to amovement sensing device 175. The knob 170 is biased (e.g., by a springreturn) to an at-rest position P(AR) between opposing rotational rangesof motion R(R), R(L). A first one of the opposing rotational ranges ofmotion R(R) is substantially equal to a second one of the opposingrotational ranges of motion R(L), R(R). To provide a tactile indicationof an amount of rotation of the knob 170, a force that biases the knob170 toward the at-rest position P(AR) can increase (e.g., non-linearly)as a function of the amount of rotation of the knob 170 with respect tothe at-rest position P(AR). Additionally, the knob 170 can be configuredwith position indicating detents such that the driver can positivelyfeel the at-rest position P(AR) and feel the ends of the opposingrotational ranges of motion R(L), R(R) approaching (e.g., soft endstops).

The movement sensing device 175 is configured for sensing movement ofthe knob 170 and outputting a corresponding signal (i.e., movementsensing device signal) to the trailer assist backup input apparatus 125shown in FIG. 1. The movement sensing device signal is generated as afunction of an amount of rotation of the knob 170 with respect to theat-rest position P(AR), a rate movement of the knob 170, and/or adirection of movement of the knob 170 with respect to the at-restposition P(AR). As will be discussed below in greater detail, theat-rest position P(AR) of the knob 170 corresponds to a movement sensingdevice signal indicating that the vehicle 100 should be steered suchthat the trailer 110 is backed along a substantially straight path (zerotrailer curvature request from the driver) as defined by a centerlinelongitudinal axis of the trailer 110 when the knob 170 was returned tothe at-rest position P(AR) and a maximum clockwise and anti-clockwiseposition of the knob 170 (i.e., limits of the opposing rotational rangesof motion R(R), R(L)) each correspond to a respective movement sensingdevice signal indicating a tightest radius of curvature (i.e., mostacute trajectory) of a path of travel of the trailer 110 that ispossible without the corresponding vehicle steering information causinga jackknife condition. In this regard, the at-rest position P(AR) is azero curvature commanding position with respect to the opposingrotational ranges of motion R(R), R(L). It is disclosed herein that aratio of a commanded curvature of a path of a trailer (e.g., radius of atrailer trajectory) and a corresponding amount of rotation of the knobcan vary (e.g., non-linearly) over each one of the opposing rotationalranges of motion P(L), P(R) of the knob 170. It is also disclosedtherein that the ratio can be a function of vehicle speed, trailergeometry, vehicle geometry, hitch geometry and/or trailer load.

Use of the knob 170 decouples trailer steering inputs from being made ata steering wheel of the vehicle 100. In use, as a driver of the vehicle100 backs the trailer 110, the driver can turn the knob 170 to indicatea desired curvature of a path of the trailer 110 to follow and returnsthe knob 170 to the at-rest position P(AR) for causing the trailer 110to be backed along a straight line. Accordingly, in embodiments oftrailer backup assist systems where the steering wheel remainsphysically coupled to the steerable wheels of a vehicle during backup ofan attached trailer, a rotatable control element configured inaccordance with the disclosed subject matter (e.g., the knob 170)provides a simple and user-friendly means of allowing a driver of avehicle to input trailer steering commands.

It is disclosed herein that a rotational control input device configuredin accordance with embodiments of the disclosed subject matter (e.g.,the knob 170 and associated movement sensing device) can omit a meansfor being biased to an at-rest position between opposing rotationalranges of motion. Lack of such biasing allows a current rotationalposition of the rotational control input device to be maintained untilthe rotational control input device is manually moved to a differentposition. Preferably, but not necessarily, when such biasing is omitted,a means is provided for indicating that the rotational control inputdevice is positioned in a zero curvature commanding position (e.g., atthe same position as the at-rest position in embodiments where therotational control input device is biased). Examples of means forindicating that the rotational control input device is positioned in thezero curvature commanding position include, but are not limited to, adetent that the rotational control input device engages when in the zerocurvature commanding position, a visual marking indicating that therotational control input device is in the zero curvature commandingposition, an active vibratory signal indicating that the rotationalcontrol input device is in or approaching the zero curvature commandingposition, an audible message indicating that the rotational controlinput device is in of approaching the zero curvature commandingposition, and the like.

It is also disclosed herein that embodiments of the disclosed subjectmatter can be configured with a control input device that is notrotational (i.e., a non-rotational control input device). Similar to arotational control input device configured in accordance withembodiments of the disclosed subject matter (e.g., the knob 170 andassociated movement sensing device), such a non-rotational control inputdevice is configured to selectively provide a signal causing a trailerto follow a path of travel segment that is substantially straight and toselectively provide a signal causing the trailer to follow a path oftravel segment that is substantially curved. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input path of travelcommands, or joystick type input and the like.

The trailer backup steering input apparatus 125 can be configured toprovide various feedback information to a driver of the vehicle 100.Examples of situation that such feedback information can include, butare not limited to, a status of the trailer backup assist system 105(e.g., active, in standby (e.g., when driving forward to reduce thehitch angle and zero hitch angle to remove bias), faulted, inactive,etc.), that a curvature limit has been reached (i.e., maximum commandedcurvature of a path of travel of the trailer 110), and/or a graphicalrepresentation of the vehicle and trailer orientation state. To thisend, the trailer backup steering input apparatus 125 can be configuredto provide a tactile feedback signal (e.g., a vibration through the knob170) as a warning if any one of a variety of conditions occur. Examplesof such conditions include, but are not limited to, the trailer 110approaching jackknife, the trailer backup assist system 105 has had afailure, the trailer backup assist system 105 has detected a fault, thetrailer backup assist system 105 or other system of the vehicle 100 haspredicted a collision on the present path of travel of the trailer 110,the trailer backup system 105 has restricted a commanded curvature of atrailer's path of travel (e.g., due to excessive speed or accelerationof the vehicle 100), and the like. Still further, it is disclosed thatthe trailer backup steering input apparatus 125 can use illumination(e.g., an LED 180) and/or an audible signal output (e.g., an audibleoutput device 185 or through attached vehicle audio speakers) to providecertain feedback information (e.g., notification/warning of anunacceptable trailer backup condition).

Referring now to FIGS. 2 and 3, an example of using the trailer backupsteering input apparatus 125 for dictating a curvature of a path oftravel (POT) of a trailer (i.e., the trailer 110 shown in FIG. 1) whilebacking up the trailer with a vehicle (i.e., the vehicle 100 in FIGS. 1and 2) is shown. In preparation of backing the trailer 110, the driverof the vehicle 100 drives the vehicle 100 forward along a pull-thru path(PTP) to position the vehicle 100 and trailer 110 at a first backupposition B1. In the first backup position B1, the vehicle 100 andtrailer 110 are longitudinally aligned with each other such that alongitudinal centerline axis L1 of the vehicle 100 is aligned with(e.g., parallel with or coincidental with) a longitudinal centerlineaxis L2 of the trailer 110. It is disclosed herein that such alignmentof the longitudinal axes L1, L2 at the onset of an instance of trailerbackup functionality is not a requirement for operability of a trailerbackup assist system configured in accordance with the disclosed subjectmatter.

After activating the trailer backup assist system 105 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 110 by reversing the vehicle 100 from the first backup positionB1. So long as the knob 170 of the trailer backup steering inputapparatus 125 remains in the at-rest position P(AR), the trailer backupassist system 105 will steer the vehicle 100 as necessary for causingthe trailer 110 to be backed along a substantially straight path oftravel as defined by the longitudinal centerline axis L2 of the trailer110 at the time when backing of the trailer 110 began. When the trailerreaches the second backup position B2, the driver rotates the knob 170to command the trailer 110 to be steered to the right (i.e., a knobposition R(R) clockwise rotation). Accordingly, the trailer backupassist system 105 will steer the vehicle 100 for causing the trailer 110to be steered to the right as a function of an amount of rotation of theknob 170 with respect to the at-rest position P(AR), a rate movement ofthe knob 170, and/or a direction of movement of the knob 170 withrespect to the at-rest position P(AR). Similarly, the trailer 110 can becommanded to steer to the left by rotating the knob 170 to the left.When the trailer reaches backup position B3, the driver allows the knob170 to return to the at-rest position P(AR) thereby causing the trailerbackup assist system 105 to steer the vehicle 100 as necessary forcausing the trailer 110 to be backed along a substantially straight pathof travel as defined by the longitudinal centerline axis L2 of thetrailer 110 at the time when the knob 170 was returned to the at-restposition P(AR). Thereafter, the trailer backup assist system 105 steersthe vehicle 100 as necessary for causing the trailer 110 to be backedalong this substantially straight path to the fourth backup position B4.In this regard, arcuate portions of a path of travel POT of the trailer110 are dictated by rotation of the knob 170 and straight portions ofthe path of travel POT are dictated by an orientation of the centerlinelongitudinal axis L2 of the trailer when the knob 170 is in/returned tothe at-rest position P(AR).

In order to activate the trailer backup assist system described above inFIGS. 1-3, the driver interacts with the trailer backup assist systemand the trailer backup assist system interacts with the vehicleenvironment. The trailer backup assist system automatically steers asthe driver reverses the vehicle. As discussed above, the driver controlsthe trailer trajectory by using a steering knob to input desired trailercurvature. The trailer backup assist algorithm determines the vehiclesteering angle to achieve the desired trailer curvature, and the drivercontrols the throttle and brake while the trailer backup assist systemcontrols the steering.

FIG. 4 shows a method 200 for implementing trailer backup assistfunctionality in accordance with one embodiment. In a preferredembodiment, the method 200 for implementing trailer backup assistfunctionality can be carried out using the trailer backup assistarchitecture discussed above in reference to the vehicle 100 and trailer110 of FIG. 1. Accordingly, trailer steering information is providedthrough use of a rotational control input device (e.g., the knob 170discussed in reference to FIG. 2).

An operation 202 is performed for receiving a trailer backup assistrequest. Examples of receiving the trailer backup assist request includeactivating the trailer backup assist system and providing confirmationthat the vehicle and trailer are ready to be backed. After receiving atrailer backup assist request (i.e., while the vehicle is beingreversed), an operation 204 is performed for receiving a trailer backupinformation signal. Examples of information carried by the trailerbackup information signal include, but are not limited to, informationfrom the trailer backup steering input apparatus 125, information fromthe hitch angle detection apparatus 130, information from the powersteering assist control module 135, information from the brake systemcontrol module 145, and information from the powertrain control module150. It is disclosed herein that information from the trailer backupsteering input apparatus 125 preferably includes trailer path curvatureinformation characterizing a desired curvature for the path of travel ofthe trailer, such as provided by the trailer backup steering inputapparatus 125 discussed above in reference to FIGS. 1 and 2. In thismanner, the operation 204 for receiving the trailer backup informationsignal can include receiving trailer path curvature informationcharacterizing the desired curvature for the path of travel of thetrailer.

If the trailer backup information signal indicates that a change incurvature of the trailer's path of travel is requested (i.e., commandedvia the knob 170), an operation 206 is performed for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel. Otherwise, an operation 208 is performedfor determining vehicle steering information for maintaining a currentstraight-line heading of the trailer (i.e., as defined by thelongitudinal centerline axis of the trailer). Thereafter, an operation210 is performed for providing the vehicle steering information to apower steering assist system of the vehicle, followed by an operation212 being performed for determining the trailer backup assist status. Ifit is determined that trailer backup is complete, an operation 214 isperformed for ending the current trailer backup assist instance.Otherwise the method 200 returns to the operation 204 for receivingtrailer backup information. Preferably, the operation for receiving thetrailer backup information signal, determining the vehicle steeringinformation, providing the vehicle steering information, and determiningthe trailer backup assist status are performed in a monitoring fashion(e.g., at a high rate of speed of a digital data processing device).Accordingly, unless it is determined that reversing of the vehicle forbacking the trailer is completed (e.g., due to the vehicle having beensuccessfully backed to a desired location during a trailer backup assistinstance, the vehicle having to be pulled forward to begin anothertrailer backup assist instance, etc.), the method 200 will continuallybe performing the operations for receiving the trailer backupinformation signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status.

It is disclosed herein that the operation 206 for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel preferably includes determining vehiclesteering information as a function of trailer path curvature informationcontained within the trailer backup information signal. As will bediscussed below in greater detail, determining vehicle steeringinformation can be accomplished through a low order kinematic modeldefined by the vehicle and the trailer. Through such a model, arelationship between the trailer path curvature and commanded steeringangles of steered wheels of the vehicle can be generated for determiningsteering angle changes of the steered wheels for achieving a specifiedtrailer path curvature. In this manner, the operation 206 fordetermining vehicle steering information can be configured forgenerating information necessary for providing trailer path curvaturecontrol in accordance with the disclosed subject matter.

In some embodiments of the disclosed subject matter, the operation 210for providing the vehicle steering information to the power steeringassist system of the vehicle causes the steering system to generate acorresponding steering command as a function of the vehicle steeringinformation. The steering command is interpretable by the steeringsystem and is configured for causing the steering system to move steeredwheels of the steering system for achieving a steered angle as specifiedby the vehicle steering information. Alternatively, the steering commandcan be generated by a controller, module or computer external to thesteering system (e.g., a trailer backup assist control module) and beprovided to the steering system.

In parallel with performing the operations for receiving the trailerbackup information signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status, the method 200 performs an operation 216 formonitoring the trailer backup information for determining if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle todetermine if a hitch angle threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determine if a vehicle steering anglethreshold is exceeded, assessing other operating parameters (e.g.,vehicle longitudinal acceleration, throttle pedal demand rate and hitchangle rate) for determining if a respective threshold value is exceeded,and the like. Backup speed can be determined from wheel speedinformation obtained from one or more wheel speed sensors of thevehicle. If it is determined that an unacceptable trailer backupcondition exists, an operation 218 is performed for causing the currentpath of travel of the trailer to be inhibited (e.g., stopping motion ofthe vehicle), followed by the operation 214 being performed for endingthe current trailer backup assist instance. It is disclosed herein thatprior to and/or in conjunction with causing the current trailer path tobe inhibited, one or more actions (e.g., operations) can be implementedfor providing the driver with feedback (e.g., a warning) that such anunacceptable hitch angle condition is impending or approaching. In oneexample, if such feedback results in the unacceptable hitch anglecondition being remedied prior to achieving a critical condition, themethod can continue with providing trailer backup assist functionalityin accordance with operations 204-212. Otherwise, the method can proceedto operation 214 for ending the current trailer backup assist instance.In conjunction with performing the operation 214 for ending the currenttrailer backup assist instance, an operation can be performed forcontrolling movement of the vehicle to correct or limit a jackknifecondition (e.g., steering the vehicle, decelerating the vehicle,limiting magnitude and/or rate of driver requested trailer curvatureinput, limiting magnitude and/or rate of the steering command, and/orthe like to preclude the hitch angle from being exceeded).

Curvature Control Algorithm

Turning now to a discussion of a kinematic model used to calculate arelationship between a curvature of a path of travel of a trailer andthe steering angle of a vehicle towing the trailer, a low orderkinematic model can be desirable for a trailer backup assist systemconfigured in accordance with some embodiments. To achieve such a loworder kinematic model, certain assumptions are made with regard toparameters associated with the vehicle/trailer system. Examples of suchassumptions include, but are not limited to, the trailer being backed bythe vehicle at a relatively low speed, wheels of the vehicle and thetrailer having negligible (e.g., no) slip, tires of the vehicle havingnegligible (e.g., no) lateral compliance, tires of the vehicle and thetrailer having negligible (e.g., no) deformation, actuator dynamics ofthe vehicle being negligible, the vehicle and the trailer exhibitingnegligible (e.g., no) roll or pitch motions.

As shown in FIG. 5, for a system defined by a vehicle 302 and a trailer304, the kinematic model 300 is based on various parameters associatedwith the vehicle 302 and the trailer 304. These kinematic modelparameters include:

δ: steering angle at steered front wheels 306 of the vehicle 302;

α: yaw angle of the vehicle 302;

β: yaw angle of the trailer 304;

γ: hitch angle (γ=β−α);

W: wheel base of the vehicle 302;

L: length between hitch point 308 and rear axle 310 of the vehicle 302;

D: length between hitch point 308 and axle length 312 of the trailer 304(axle length 312 may be an effective, or equivalent, axle length for atrailer having a multiple axle configuration; and

r₂: curvature radius for the trailer 304.

The kinematic model 300 of FIG. 5 reveals a relationship between trailerpath radius of curvature r₂ at the midpoint 314 of an axle 312 of thetrailer 304, steering angle δ of the steered wheels 306 of the vehicle302, and the hitch angle γ. As shown in the equation below, thisrelationship can be expressed to provide the trailer path curvature κ₂is such that, if γ is given, the trailer path curvature κ₂ can becontrolled based on regulating the steering angle δ (where {dot over(β)} is trailer yaw rate and {dot over (η)} is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2\;}} = {\frac{\overset{.}{\beta}}{\overset{.}{\eta}} = \frac{{( {W + \frac{{KV}^{2}}{g}} )\sin \; \gamma} + {L\; \cos \; \gamma \; \tan \; \delta}}{D( {{( {W + \frac{{KV}^{2}}{g}} )\cos \; \gamma} - {L\; \sin \; \gamma \; \tan \; \delta}} )}}}$

Or, this relationship can be expressed to provide the steering angle δas a function of trailer path curvature κ₂ and hitch angle γ.

$g = {{\tan^{- 1}( \frac{( {W + \frac{{KV}^{2}}{g}} )\lbrack {{\kappa_{2}D\; \cos \; \gamma} - {\sin \; \gamma}} \rbrack}{{{DL}\; \kappa_{2}\sin \; \gamma} + {L\; \cos \; \gamma}} )} = {F( {\gamma,\kappa_{2},K} )}}$

Accordingly, for a particular vehicle and trailer combination, certainkinematic model parameters (e.g., D, W and L) are constant and assumedknown. V is the vehicle longitudinal speed and g is the acceleration dueto gravity. K is a speed dependent parameter which when set to zeromakes the calculation of steering angle independent of vehicle speed.For example, vehicle-specific kinematic model parameters can bepredefined in an electronic control system of a vehicle andtrailer-specific kinematic model parameters can be inputted by a driverof the vehicle. Trailer path curvature κ₂ is determined from the driverinput via a trailer backup steering input apparatus. Through the use ofthe equation for providing steering angle, a corresponding steeringcommand can be generated for controlling a steering system (e.g., anactuator thereof) of the vehicle.

FIG. 6 shown an example of a trailer path curvature function plot 400for a rotary-type trailer backup steering input apparatus (e.g., thetrailer backup steering input apparatus 125 discussed above in referenceto FIGS. 1 and 2). A value representing trailer path curvature (e.g.,trailer path curvature κ2) is provided as an output signal from therotary-type trailer backup steering input apparatus as a function ofuser input movement. In this example, a curve 402 specifying trailerpath curvature relative to user input (e.g., amount of rotation) at arotary input device (e.g., a knob) is defined by a cubic function.However, a skilled person will appreciate that embodiments of thedisclosed subject matter are not limited to any particular functionbetween a magnitude and/or rate of input at a trailer backup steeringinput apparatus (e.g., knob rotation) and a resulting trailer pathcurvature value.

Jackknife Detection

Referring to FIG. 5, in preferred embodiments of the disclosed subjectmatter, it is desirable to limit the potential for the vehicle 302 andthe trailer 304 to attain a jackknife angle (i.e., the vehicle/trailersystem achieving a jackknife condition). A jackknife angle γ(j) refersto a hitch angle γ that while backing cannot be overcome by the maximumsteering input for a vehicle such as, for example, the steered frontwheels 306 of the vehicle 302 being moved to a maximum steered angle δat a maximum rate of steering angle change. The jackknife angle γ(j) isa function of a maximum wheel angle for the steered wheel 306 of thevehicle 302, the wheel base W of the vehicle 302, the distance L betweenhitch point 308 and the rear axle 310 of the vehicle 302, and the lengthD between the hitch point 308 and the effective axle 312 of the trailer304 when the trailer has multiple axles. The effective axle 312 may bethe actual axle for a single axle trailer or an effective axle locationfor a trailer with multiple axles. When the hitch angle γ for thevehicle 302 and the trailer 304 achieves or exceeds the jackknife angleγ(j), the vehicle 302 must be pulled forward to reduce the hitch angleγ. Thus, for limiting the potential for a vehicle/trailer systemattaining a jackknife angle, it is preferable to control the yaw angleof the trailer while keeping the hitch angle of the vehicle/trailersystem relatively small.

Referring to FIGS. 5 and 7, a steering angle limit for the steered frontwheels 306 requires that the hitch angle γ cannot exceed the jackknifeangle γ(j), which is also referred to as a critical hitch angle. Thus,under the limitation that the hitch angle γ cannot exceed the jackknifeangle γ(j), the jackknife angle γ(j) is the hitch angle γ that maintainsa circular motion for the vehicle/trailer system when the steered wheels306 are at a maximum steering angle δ(max). The steering angle forcircular motion with hitch angle is defined by the following equation.

${\tan \; \delta_{{ma}\; x}} = \frac{w\; \sin \; \gamma_{m\; {ax}}}{D + {L\; \cos \; \gamma_{{ma}\; x}}}$

Solving the above equation for hitch angle allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the disclosed subject matter formonitoring hitch angle in relation to jackknife angle.

${\cos \; \overset{\_}{\gamma}} = \frac{{- b} \pm \sqrt{b^{2} - {4a\; c}}}{2a}$

where,

a=L ² tan²δ(max)+W ²;

b=2LD tan²δ(max); and

c=D ² tan²δ(max)−W ².

In certain instances of backing a trailer, a jackknife enablingcondition can arise based on current operating parameters of a vehiclein combination with a corresponding hitch angle. This condition can beindicated when one or more specified vehicle operating thresholds aremet while a particular hitch angle is present. For example, although theparticular hitch angle is not currently at the jackknife angle for thevehicle and attached trailer, certain vehicle operating parameters canlead to a rapid (e.g., uncontrolled) transition of the hitch angle tothe jackknife angle for a current commanded trailer path curvatureand/or can reduce an ability to steer the trailer away from thejackknife angle. One reason for a jackknife enabling condition is thattrailer curvature control mechanisms (e.g., those in accordance with thedisclosed subject matter) generally calculate steering commands at aninstantaneous point in time during backing of a trailer. However, thesecalculations will typically not account for lag in the steering controlsystem of the vehicle (e.g., lag in a steering EPAS controller). Anotherreason for the jackknife enabling condition is that trailer curvaturecontrol mechanisms generally exhibit reduced steering sensitivity and/oreffectiveness when the vehicle is at relatively high speeds and/or whenundergoing relatively high acceleration.

Jackknife Countermeasures

FIG. 8 shows a method 500 for implementing jackknife countermeasuresfunctionality in accordance with an embodiment of the disclosed subjectmatter for a vehicle and attached trailer. Trailer backup assistfunctionality in accordance with the disclosed subject matter caninclude jackknife countermeasures functionality. Alternatively,jackknife countermeasures functionality in accordance with oneembodiment can be implemented separately from other aspects of trailerbackup assist functionality.

The method 500 begins when operation 502 is performed for receivingjackknife determining information characterizing a jackknife enablingcondition of the vehicle-trailer combination at a particular point intime (e.g., at the point in time when the jackknife determininginformation was sampled). Examples of the jackknife determininginformation includes, but are not limited to, information characterizinga hitch angle, information characterizing a vehicle accelerator pedaltransient state, information characterizing a speed of the vehicle,information characterizing longitudinal acceleration of the vehicle,information characterizing a brake torque being applied by a brakesystem of the vehicle, information characterizing a powertrain torquebeing applied to driven wheels of the vehicle, and informationcharacterizing the magnitude and rate of driver requested trailercurvature. The operation 502 for receiving jackknife determininginformation can be the first operation in a sampling process wherejackknife determining information is sampled upon initiation of aninstance of implementing jackknife countermeasures functionality. Inthis regard, jackknife determining information would be continuallymonitored such as, for example, by an electronic control unit (ECU) thatcarries out trailer backup assist (TBA) functionality. As discussedabove in reference to FIG. 5, a kinematic model representation of thevehicle and the trailer can be used to determine a jackknife angle forthe vehicle-trailer combination. However, the disclosed subject matteris not unnecessarily limited to any specific approach for determiningthe jackknife angle.

After receiving the jackknife determining information, an operation 504is performed for assessing the jackknife determining information fordetermining if the vehicle-trailer combination attained the jackknifeenabling condition at the particular point in time. The objective of theoperation 504 for assessing the jackknife determining information isdetermining if a jackknife enabling condition has been attained at thepoint in time defined by the jackknife determining information. If it isdetermined that a jackknife enabling condition is not present at theparticular point in time, the method 500 returns to the operation 502for receiving another instance of the jackknife determining information.If it is determined that a jackknife enabling condition is present atthe particular point in time, an operation 506 is performed fordetermining an applicable countermeasure or countermeasures toimplement. Accordingly, in some embodiments, an applicablecountermeasure will be selected dependent upon a parameter identified asbeing a key influencer of the jackknife enabling condition. However, inother embodiments, an applicable countermeasure will be selected asbeing most able to readily alleviate the jackknife enabling condition.In still other embodiment, a predefined countermeasure or predefined setof countermeasures may be the applicable countermeasure(s).

The objective of a countermeasure in the context of the disclosedsubject matter (i.e., a jackknife reduction countermeasure) is toalleviate a jackknife enabling condition. To this end, such acountermeasure can be configured to alleviate the jackknife enablingcondition using a variety of different strategies. In a vehicle speedsensitive countermeasure strategy, actions taken for alleviating thejackknife enabling condition can include overriding and/or limitingdriver requested trailer radius of curvature (e.g., being requested viaa trailer backup steering input apparatus configured in accordance withthe disclosed subject matter) as a function of vehicle speed (e.g., viaa lookup table correlating radius of curvature limits to vehicle speedas shown in FIG. 6). In a countermeasure strategy where trailercurvature requests are limited as a function of speed and drivercurvature command transient rates, actions taken for alleviating thejackknife enabling condition can include rate limiting trailer curvaturecommand transients as requested by a driver above a predefined vehiclespeed whereas, under the predefined vehicle speed, the as-requestedtrailer curvature are not rate limited. In a torque limitingcountermeasure strategy, actions taken for alleviating the jackknifeenabling condition can include application of full available powertraintorque being inhibited when the jackknife enabling condition is presentwhile the vehicle is above a predefined speed and application of fullavailable powertrain torque being allowed when the vehicle speed isreduced below the predefined speed while in the torque inhibiting mode.As opposed to a fixed predefined speed, the torque limitingcountermeasure strategy can utilize a speed threshold that is a functionof hitch angle (i.e., speed threshold inversely proportional to hitchangle acuteness). In a driver accelerator pedal transient detectioncountermeasure strategy, actions taken for alleviating the jackknifeenabling condition can include overriding and/or limiting driverrequested trailer radius of curvature as a function of transientaccelerator pedal requests (e.g., requested trailer radius of curvaturelimited when a large accelerator pedal transient is detected). In ahitch angle rate sensitive countermeasure strategy, actions taken foralleviating the jackknife enabling condition can include using hitchangle rate in a predefined or calculated mapping with current hitchangle position to limit driver requested trailer radius of curvature.Accordingly, in view of the disclosures made herein, a skilled personwill appreciate that embodiments of the disclosed subject matter are notunnecessarily limited to a countermeasure strategy of any particularconfiguration.

As disclosed above, implementation of trailer backup assistfunctionality in accordance with the disclosed subject matter canutilize a kinematic model for determining steering control information,jackknife enabling conditions, and jackknife angle. Such a kinematicmodel has many parameters than can influence trailer curvature controleffectiveness. Examples of these parameters include, but are not limitedto, the vehicle wheelbase, understeer gradient gain, vehicle trackwidth, maximum steer angle at the vehicle front wheels, minimum turningradius of vehicle, maximum steering rate able to be commanded by thesteering system, hitch ball to trailer axle length, and vehicle rearaxle to hitch ball length. Sensitivity analysis for a given kinematicmodel can be used to provide an understanding (e.g., sensitivity) of therelationships between such parameters, thereby providing informationnecessary for improving curvature control performance and for reducingthe potential for jackknife enabling conditions. For example, through anunderstanding of the sensitivity of the parameters of a kinematic model,scaling factors can be used with speed dependent jackknifecountermeasures to reduce jackknife potential (e.g., for specialapplications such as short wheelbase conditions).

Still referring to FIG. 8, after determining the applicablecountermeasure(s), an operation 508 is performed for implementing thechosen jackknife countermeasure(s) and an operation 510 is performed forinitiating a jackknife warning. As discussed above in regard tocountermeasure strategies, implementing the jackknife countermeasure(s)can include commanding a speed controlling system of the vehicle totransition to an altered state of operation in which a speed of thevehicle is reduced, commanding the steering control system of thevehicle to transition to an altered state of operation in which a radiusof curvature of a path of the trailer is increased, command the steeringcontrol system of the vehicle to transition to an altered state ofoperation in which a decrease in the radius of the curvature of the pathof the trailer is inhibited, commanding a brake control system of thevehicle to apply brake torque to reduce vehicle speed/inhibit vehicleacceleration, and/or commanding a powertrain control system of thevehicle to inhibit full available powertrain torque from being deliveredto driven wheels of the vehicle until another jackknife enablingparameter (e.g., vehicle speed) is below a defined threshold. In certainembodiments of the disclosed subject matter, the jackknife warning isprovided to the driver using at least one vehicle control system throughwhich the jackknife countermeasure is implemented. Speed reduction, inaddition to applying the brakes, can be accomplished by any number ofmeans such as, for example, limiting throttle inputs (e.g., via aterrain management feature) and/or transitioning a transmission to areverse low gear if the vehicle is equipped with a multi-range reversegear transmission. Examples of such system-specific warning approachinclude, but are not limited to, providing a warning through anaccelerator pedal of the vehicle (e.g., via haptic feedback) if thecountermeasure includes limiting speed of the vehicle and/or providing awarning through an input element (e.g., knob) of a trailer backupsteering input apparatus of the vehicle (e.g., via haptic feedback ifthe countermeasure includes limiting driver requested trailer radius ofcurvature), through haptic seat vibration warning, through a visualwarning (e.g., through a visual display apparatus of the towing vehicle)and/or through audible warnings (e.g., through an audio output apparatusof the towing vehicle), or the like. One embodiment of utilizingwarnings relating to vehicle speed as it relates to onset or presence ofa jackknife enabling condition includes implementation of a dual stagewarning. For example, when a backing speed of the vehicle increasessufficiently for causing a speed of the vehicle to reach a lower (i.e.,first) speed threshold during backing of the trailer, a driver of thevehicle would be provided with a first warning indication (e.g., viahaptic, audible, and/or visual means as implemented by the trailerbackup assist system) for informing the driver that there is the need toreduce the speed of the vehicle to alleviate or preclude the jackknifeenabling condition. If the driver does not correspondingly respond bycausing a speed of the vehicle to be reduced (or not to furtherincrease) and the vehicle continues to gain speed such that it passes ahigher (i.e., a second) speed threshold, the driver of the vehicle wouldbe provided with a second warning indication (e.g., a more severehaptic, audible, and/or visual means as implemented by the trailerbackup assist system) for informing the driver that there is animmediate need to reduce the speed of the vehicle to alleviate orpreclude the jackknife enabling condition. The first and/or the secondspeed indication warnings can be implemented in conjunction with arespective speed limiting countermeasure measures (e.g., the trailerbackup assist system causing activation of a brake system of the vehicleand/or reducing a throttle position of the vehicle).

Human Machine Interface

In order to implement the control features discussed above with respectto methods described in FIG. 5 and FIG. 8, a driver must interact withthe trailer backup assist system 105 to configure the system 105. Thevehicle 100 is also equipped, as shown in FIG. 9, with a human machineinterface (HMI) device 102 to implement trailer backup assistfunctionality through driver interaction with the HMI device 102.

FIG. 9 shows an example of an HMI device 102 in the vehicle that adriver uses to interact with the trailer backup assist system 105. Thedriver is presented with multiple menus 104 (only one example menu isshown in FIG. 9) displayed by way of the HMI 102. The HMI menus 104assist the driver through modules (shown in FIGS. 10 and 11) that setup600, calibrate 700, and activate 800 the trailer backup assist system105 so that control methods 200, 500 may be implemented to assist thedriver with the backup of the trailer shown generally as a flow diagramin FIGS. 10 and 11, and to be discussed in greater detail later herein.Each module is directed to particular elements, or features, which areused to configure the trailer backup assist system to accuratelyimplement control methods 200, 500. While each module is described withreference to particular features of the disclosed subject matter, itshould be noted that each module is not necessarily limited to theparticular features described in the examples herein. It is possible torearrange the modules or to replace elements or features of a modulewithout departing from the scope of the disclosed subject matter.

The trailer backup assist system 105 will guide a driver through thesteps necessary to connect a trailer and attach a target. The driver mayactivate the setup by way of the backup steering input apparatus 125,for example by turning or pushing the rotary knob, or my merely making aselection for the trailer backup assist system from a menu on the HMIdevice 102. Referring to FIG. 10, a driver initiates the trailer backupassist system through the trailer backup assist steering inputapparatus. In the case of a rotary knob, the driver presses or rotatesthe knob to initiate the trailer backup assist system. The system willguide the driver through the steps of connecting 580 a compatibletrailer 110. A compatible trailer is one that pivots at a single pointrelative to the vehicle and behind the rear axle of the vehicle.

Once the system is selected by either the trailer backup steering inputapparatus 125 or the HMI device 102, the system will guide the driver toprepare the vehicle and vehicle trailer combination as necessary. Thevehicle 100 should be turned “on” and the vehicle 100 should be in“park” 590. In the event the vehicle 100 is on but is traveling at aspeed that is greater than a predetermined limit, for example five milesper hour, the trailer backup assist system 105 will become inactive andinaccessible to the driver. The trailer backup assist system 105 setupmodule 600 will not begin or will be exited 585. If the type of trailer110 selected by the driver is a trailer 110 that is not compatible withthe trailer backup assist system 105, the setup module 600 will beexited 585 or will not begin. In the event, the trailer 110 iscompatible with the trailer backup assist system 105, the setup module600 verifies that the vehicle 100 gear shift mechanism is in “park.”Again, in the event the vehicle is not “on” and the gear shift mechanismis not on “park,” the setup module will not begin 585.

Upon connection 580 of a compatible trailer 110, the vehicle 100 being“on” 590 and the vehicle 100 being in “park” 590, the HMI 102 willpresent a menu 104 that has a “Towing” mode option to be selected by thedriver. The driver selects “Towing” mode and a menu 104 is presentedthat provides a “Trailer Options” selection. The driver then selects a“Trailer Options” mode from the “Towing” menu. The driver is prompted toeither “add a trailer” or “select a trailer” from a menu 104 presentedon the HMI device and the “Setup” module 600 has begun. For certaincamera-based hitch angle detection systems, an operation 602 isperformed wherein a warning menu may be presented to the driver, by wayof the HMI, informing the driver that the trailer must be in a straightline, meaning there is no angle at the hitch between the vehicle and thetrailer. The warning indicates that the driver may need to takecorrective action, for example, pull the vehicle forward in order toalign the trailer and the vehicle as required for the setup 600. Ageneric or static graphic may be presented by way of the HMI 102 toassist the driver in visually recognizing the alignment between thetrailer 110 and the vehicle 100 that is necessary in order to properlysetup and calibrate the trailer backup assist system 105. The driverapplies any corrections 603 in that the driver makes any necessaryadjustment he has been alerted to and indicates, by acknowledging thatcorrective actions have been applied 603 and that the trailer is in linewith the vehicle. Other hitch angle detection systems may not need thedriver to straighten the trailer during setup mode.

To aid the driver in the setup process, the reverse back lights, or anyother supplemental lighting that may be available on the vehicle, areilluminated 604. In the event the trailer is a new trailer, one that hasnot been attached to the vehicle before or has not been previouslystored in the trailer backup assist system, the driver is presented 606with an option to either name the trailer or select a previously storedtrailer configuration. Naming the trailer 608 allows the trailer to beeasily identified the next time it is attached to the vehicle so thatthe driver does not have to repeat the setup process. The driver eitherenters a unique name to identify the trailer that is to be stored in thetrailer backup assist system or selects a previously stored trailerconfiguration associated with the attached trailer. The trailer backupassist system will not allow more than one trailer to have the samename. Therefore, if a driver attempts to name a trailer using a namethat has already been applied to a previously stored trailerconfiguration, the HMI will display a message to the driver indicatingso and requesting the driver enter a different name for the trailerconfiguration. In the case where a previously stored trailerconfiguration is available and selected 610 by the driver, certain stepsin the setup process may be skipped.

The following discussion is directed to a first time trailerconfiguration for a camera-based hitch angle detection system. Thedriver is instructed 612 to place a hitch angle target on the trailerthat is used for calibration purposes. A generic static image may bedisplayed on the HMI that provides direction to the driver as toplacement of a target on the trailer that is used for hitch angledetection. The target placement is dependent upon the type of trailerbeing towed and therefore, options may be presented to the driver to aidthe driver in selecting an appropriate trailer type. The static imagemay indicate areas that are acceptable for target placement as well asareas that are unacceptable for target placement. The static imageindicating the appropriate areas for attaching the target may be anoverlay of the rear view of the trailer hitch. Once the driver attachesthe target to the trailer and indicates by way of the HMI that thetarget has been attached to the trailer the setup mode provides 614visual feedback to the driver identifying that the target has beenlocated, or acquired. The driver acknowledges 616, by way of the HMI,that the target has been properly identified by the trailer backupassist system. Similarly, for a previously stored trailer configuration,the trailer will already have a target placed thereon. The trailerbackup assist system will acquire the target and provide 614 visualfeedback to the driver confirming acquisition of the target.

In the event the target is not acquired 614 after a predetermined amountof time lapses, the driver is notified 618 of the need to reposition thetarget and presented with possible corrective measures that may betaken. Possible corrective measures may be presented to the driver suchas cleaning the camera lens, cleaning the target, replacing the targetif it has been damaged or faded, pulling the vehicle-trailer combinationforward to improve lighting conditions around the camera and/or target,and moving the target to an acceptable location. The driver applies thenecessary corrections 603. As mentioned above, some hitch angledetection systems may not require the driver to attach a target to thetrailer during set up mode. The target and acquisition of the target aredirected to camera-based hitch angle detection systems.

When the target is acquired 614 by the trailer backup assist system andthe driver has acknowledged 616 the acquisition, the driver is thenprompted through a series of menus to input 620 trailer measurementinformation that may be stored in the trailer backup assist system for atrailer configuration that is to be associated with the named trailer.The next time the same trailer is attached to the vehicle, its uniquetrailer configuration will already be stored and progress through thesetup module will be faster or, in some cases, may be skipped entirely.Generic static images may be displayed at the HMI screen in order toassist the driver with the measurement information. Visual examples, seeFIG. 12, may be provided to aid the driver in identifying the locationon the vehicle, the trailer or between the vehicle and trailer that thedriver is being prompted to enter. In addition, numerical limits for thedriver entered measurements are set within the trailer backup assistsystem and may be displayed to the driver. The driver may be warnedabout entered measurements that exceed the numerical limits.Additionally, the measurement information requests that the driver isprompted to enter may be presented to the driver in the order that themeasurements should be entered into the trailer backup assist system.

It should be noted that while measurement information is discussed aboveas being entered by the driver, various methods of entering measurementinformation may also be employed without departing from the scope of thedisclosed subject matter. For example, a system to automatically detectmeasurements using existing vehicle and trailer data including, but notlimited to, vehicle speed, wheel rotation, steering wheel angle, vehicleto trailer relative angle, and a rate of change of the vehicle to hitchangle.

Examples of the measurement information may include a horizontaldistance from the rear of the vehicle to the center of a hitch ball, ahorizontal distance from the rear of the vehicle to a center of thetarget, a vertical distance from the target to the ground, and ahorizontal offset of the target from a centerline of the hitch ball. Inthe event the target is attached at other than the centerline of thehitch ball, then the trailer backup assist system must know which sideof the vehicle the target is attached to, the passenger side or thedriver side. A menu on the HMI may be presented for the driver toindicate passenger side or driver side for the placement of the target.The trailer backup assist system also needs to know the horizontaldistance from the rear of the vehicle to a center of the axle or axlesof the trailer. The measurements may be entered in either English ormetric units.

The driver is presented 622 with the option to revise any of themeasurements before proceeding with the setup process. Otherwise, thesetup module 600 is complete 624 and the calibration module 700 begins.

The calibration module 700 is designed to calibrate the curvaturecontrol algorithm with the proper trailer measurements and calibrate thetrailer backup assist system for any hitch angle offset that may bepresent. After completing the setup module 600, the calibration modulebegins 700 and the driver is instructed 702 to pull the vehicle-trailercombination straight forward until a hitch angle sensor calibration iscomplete. The HMI may notify 704 the driver, by way of a pop up orscreen display that the vehicle-trailer combination needs to be pulledforward until calibration is complete. When calibration is complete, theHMI may notify 704 the driver. Any hitch angle offset value is stored706 in memory, accessed as necessary by the curvature control algorithm,and the calibration module 700 ends 704.

It should be noted that while hitch angle calibration is described aboveas may be requesting the driver pull forward information, various othermethods of hitch angle calibration may also be employed withoutdeparting from the scope of the embodiment.

Upon completion of the setup module 600 and the calibration module 700,the activation module 800 may begin. The activation module 800 isdescribed with reference to FIG. 11. The activation module 800 isdesigned to activate automatic steering of the vehicle during trailerbackup assist operations. The driver is instructed 802 to place thevehicle in reverse. Upon activation of the trailer backup assist system,the steering system will not accept any steering angle commands from anysource other than the trailer backup assist system 804. The trailersetup 600 and calibration 700 modules must be completed and a currenthitch angle must be within a predetermined operating range for thetrailer backup assist system 806. The vehicle speed must also be lessthan a predetermined activation speed 808. In the event any one, or all,of these conditions 804, 806, 808 are not met, the driver is prompted toapply a corrective measure 810. The driver must confirm 814 that thecorrective action has been taken in order for the control module tobegin. If a corrective action is taken, but the activation module deemsit unacceptable, the driver will be instructed 810 to try anothercorrective action.

For steering systems where the steering wheel is directly coupled to thesteered wheels of the vehicle, the driver cannot engage with thesteering wheel during trailer backup assist. If any steering wheelmotion is obstructed, by the driver or otherwise, the trailer backupassist system will present instructions 810 to the driver to removetheir hands from the steering wheel. Activation 800 will be suspended ordiscontinued until the obstruction is removed. If the vehicle speedexceeds a threshold speed or if the vehicle hitch angle is notacceptable, the driver will be prompted 810 to take corrective action.Until corrective action is taken, accepted and acknowledged, theactivation 800 and control 200, 500 modules will be interrupted.

When the driver moves the gear shift from “park” to “reverse” 802 andpresses or turns a trailer backup steering input apparatus 125 a rearview camera image may appear in a display of the HMI. If at any timeduring the reversing process the hitch angle becomes too large for thesystem to control the curvature of the trailer, the TBA will provide awarning to the driver to pull forward to reduce the hitch angle. If atany time during the reversing process the system is unable to track thehitch angle target, the driver is presented with instructions to correctthe problem. If at any time the vehicle speed exceeds that predeterminedactivation speed, the driver is visually and audibly warned to stop orslow down.

When all of the conditions of the activation module are met andmaintained, the control module may begin. The control module executesthe directives described above with reference to FIGS. 5 and 7. However,the activation module 800 includes a monitoring function 816 so that, ifat any time during execution of the control module 200, 500 the controlis interrupted, the driver is instructed to make necessary corrections.In the event any one of the necessary corrections is not made, thecontrol of the vehicle by way of the trailer backup assist system willend. The driver may also intentionally end the control by exiting thesystem through a menu selection on the HMI or placing the vehicle in agear setting that is other than park or reverse.

Referring now to instructions processible by a data processing device,it will be understood from the disclosures made herein that methods,processes and/or operations adapted for carrying out trailer backupassist functionality as disclosed herein are tangibly embodied bynon-transitory computer readable medium having instructions thereon thatare configured for carrying out such functionality. The instructions aretangibly embodied for carrying out the method 200, 500, 600, 700 and 800disclosed and discussed above and can be further configured for limitingthe potential for a jackknife condition such as, for example, bymonitoring jackknife angle through use of the equations discussed inreference to FIGS. 5 and 7 and/or by implementing jackknifecountermeasures functionality discussed above in reference to FIG. 8.The instructions may be accessible by one or more data processingdevices from a memory apparatus (e.g. RAM, ROM, virtual memory, harddrive memory, etc.), from an apparatus readable by a drive unit of adata processing system (e.g., a diskette, a compact disk, a tapecartridge, etc.) or both. Accordingly, embodiments of computer readablemedium in accordance with the disclosed subject matter include a compactdisk, a hard drive, RAM or other type of storage apparatus that hasimaged thereon a computer program (i.e., instructions) configured forcarrying out trailer backup assist functionality in accordance with thedisclosed subject matter.

In a preferred embodiment of the disclosed subject matter, a trailerbackup assist control module (e.g., the trailer backup assist controlmodule 120 discussed above in reference to FIG. 1) comprises such a dataprocessing device, such a non-transitory computer readable medium, andsuch instructions on the computer readable medium for carrying outtrailer backup assist functionality (e.g., in accordance with the method200 discussed above in reference to FIG. 2) and/or the method 500discussed above in reference to FIG. 8 and/or the methods 600, 700 and800 discussed above in reference to FIGS. 10 and 11. To this end, thetrailer backup assist control module can comprise various signalinterfaces for receiving and outputting signals. For example, ajackknife enabling condition detector can include a device providinghitch angle information and hitch angle calculating logic of the trailerbackup assist control module. A trailer backup assist control module inthe context of the disclosed subject matter can be any control module ofan electronic control system that provides for trailer backup assistcontrol functionality in accordance with the disclosed subject matter.Furthermore, it is disclosed herein that such a control functionalitycan be implemented within a standalone control module (physically andlogically) or can be implemented logically within two or more separatebut interconnected control modules (e.g., of an electronic controlsystem of a vehicle) In one example, trailer backup assist controlmodule in accordance with the disclosed subject matter is implementedwithin a standalone controller unit that provides only trailer backupassist functionality. In another example, trailer backup assistfunctionality in accordance with the disclosed subject matter isimplemented within a standalone controller unit of an electronic controlsystem of a vehicle that provides trailer backup assist functionality aswell as one or more other types of system control functionality of avehicle (e.g., anti-lock brake system functionality, steering powerassist functionality, etc.). In still another example, trailer backupassist functionality in accordance with the disclosed subject matter isimplemented logically in a distributed manner whereby a plurality ofcontrol units, control modules, computers, or the like (e.g., anelectronic control system) jointly carry out operations for providingsuch trailer backup assist functionality.

Trailer Target Placement and Monitoring

The vehicle trailer backup assist system may utilize a target placed onthe trailer to serve as the hitch angle detection component 155. Indoing so, the trailer backup assist system may employ informationacquired via image acquisition and processing of the target for use inthe hitch angle detection apparatus 130, according to one embodiment.According to other embodiments, the target may be used to identify if aconnected trailer has changed, trailer connection or disconnection, andother trailer related information. The target is an identifiable visualtarget that can be captured in an image by the video imaging camera anddetected and processed via image processing. According to oneembodiment, the target may include an adhesive target, also referred toas a sticker, that may be adhered via adhesive on one side onto thetrailer, preferably within a target placement zone, such that the cameraand image processing may detect the target and its location on thetrailer to determine trailer related information, such as the hitchangle between the trailer and the towing vehicle. The trailer backupassist system may provide to the user one or more image(s) of thetrailer target zone for proper placement of the target to assist withplacement of the target on the trailer. Additionally, the vehicletrailer backup assist system may monitor the target to determine if thetarget has been correctly placed within a desired target placement zoneand provide feedback alert(s) to the user. Further, the trailer backupassist system may monitor the trailer connection by monitoring thetarget to determine if the target has moved to determine whether thesame trailer remains connected to the tow vehicle, and may initiateaction in response thereto. Further, the trailer backup assist systemmay monitor the hitch angle or the target to determine if the trailermay have been changed out (i.e., disconnected and replaced with anothertrailer), and may initiate action in response thereto.

Referring to FIG. 13, the vehicle trailer backup assist system 105 isshown including the hitch angle detection apparatus 130 and a targetmonitor controller 10 for monitoring the target, assisting withplacement of the target, monitoring connection of the trailer,determining if the trailer has moved, and initiating certain actions.The target monitor controller 10 may include a microprocessor 12 and/orother analog and/or digital circuitry for processing one or moreroutines. Additionally, the target monitor controller 10 may includememory 14 for storing one or more routines including image processingroutine(s) 16, a target placement assist routine 900, a targetmonitoring routine 920, an initial setup for target moved detectionroutine 940, a target moved detection routine 960, and a trailerconnection monitoring routine 990. It should be appreciated that thetarget monitor controller 10 may be a standalone dedicated controller ormay be a shared controller integrated with other control functions, suchas integrated with the hitch angle detection apparatus 130, to processthe images of the trailer and target and perform related functionality.In one embodiment, the hitch angle detection apparatus 130 processes theacquired images of the target from the target monitor controller 10 andother information such as trailer length for use in determining thehitch angle between the trailer and the towing vehicle.

A camera 20 is shown as an input for providing video images to thetarget monitor controller 10 of the vehicle trailer backup assist system105. The camera 20 may be a rearview camera mounted on the tow vehiclein a position and orientation to acquire images of the trailer towed bythe vehicle rearward of the vehicle. The camera 20 may include animaging camera that generates one or more camera images of the trailerincluding the region where a target placement zone is expected to belocated on the trailer. The camera 20 may include a video imaging camerathat repeatedly captures successive images of the trailer for processingby the target monitor controller 10. The target monitor controller 10processes the one or more images from the camera 20 with one or moreimage processing routine(s) 16 to identify the target and its locationon the trailer. The target monitor controller 10 further processes theprocessed images in connection with one or more of routines 900, 920,940, 960 and 990.

The trailer monitor controller 10 may communicate with one or moredevices including vehicle exterior alerts 24 which may include vehiclebrake lights and vehicle emergency flashers for providing a visual alertand a vehicle horn for providing an audible alert. Additionally, thetrailer monitor controller may communicate with one or more vehiclehuman machine interfaces (HMIs) 25 including a vehicle display such as acenter stack mounted navigation/entertainment display. Further, thetrailer monitor controller 10 may communicate via wireless communication22 with one or more handheld or portable devices 26, such as one or moresmartphones. The portable device 26 may include a display 28 fordisplaying one or more images and other information to a user. Theportable device 26 may display one or more images of the trailer and thetarget location within a desired target placement zone on display 28. Inaddition, the portable device 26 may provide feedback information aboutthe vehicle target connection including visual and audible alerts.

Referring to FIGS. 14-17, the placement of the target 30 onto trailer110 using the target monitor controller 10 processing the targetplacement assist routine 900 is illustrated according to one exemplaryembodiment. In FIGS. 14 and 15, a tow vehicle 100 is shown towing atrailer 110. The trailer 110 has a trailer hitch connector in the formof a coupler assembly 114 connected to a vehicle hitch connector in theform of a receiver hitch and ball 15. The coupler assembly 114 latchesonto the hitch ball 15 to provide a pivoting ball joint. The trailer 110is shown having a frame including a longitudinally extending bar ortrailer tongue 112. A top horizontal surface of trailer tongue 112 isshown providing a desired target placement zone 32 for receiving thetarget 30. It should be appreciated that the trailer 110 may beconfigured in various shapes and sizes and may offer one or more othersuitable target placement zones 32 for receiving the target 30. Thetarget placement zone 32 defines the desired location for placement ofthe target 30.

The vehicle 100 is equipped with a video imaging camera 20 shown locatedin an upper region of the vehicle tailgate at the rear of the vehicle100. The video imaging camera 20 is elevated relative to the targetplacement zone(s) and has an imaging field of view and is located andoriented to capture one or more images of the trailer 110 including aregion containing one or more desired target placement zone(s). Itshould be appreciated that one or more cameras may be located at otherlocations on the vehicle 100 to acquire images of the trailer 110 andthe target placement zone(s) 32.

In order to utilize a target on a trailer that is not currently equippedwith a suitable pre-existing target, a user 2 may be instructed ordirected to place the target 30 onto the trailer 110 within a desiredtarget placement zone 32 so that the camera 20 may capture one or moreimages of the target 30 to determine trailer related information for thetrailer backup assist system, such as hitch angle information for thehitch angle detection apparatus 130. In doing so, a user 2 may beprompted by an audible or visual message on an HMI such as the vehicleHMI 25 or portable device 26 to place the target 30 on the trailer 110.The vehicle HMI 25 may include visual and/or audible outputs generatinginstructions for proper target placement.

To allow for efficient and proper placement of the target 30 onto thetrailer 110, the trailer backup assist system employs a target placementassist method or routine 900 shown in FIG. 17 that is processed by thetarget monitor controller 10. The target placement assist method 900includes step 902 in which a user may connect a portable device havingan image display to communicate with the vehicle. The user may connectthe device electronically to the vehicle which can be achieved by way ofa wireless protocol, according to one embodiment. The device may be awireless device that may communicate via Wi-Fi, BLUETOOTH® or otherwireless protocol. Alternatively, the device could be connected via awired connection. Next, at step 904, the user initiates the hitch angledetection system setup which requires initiating the setup procedure forthe hitch angle detection system. As part of this procedure, the userwill be required to place a target onto the trailer of the vehiclewithin a target placement zone. At step 906, the system generates withthe camera one or more images of the towed trailer which include aregion where the desired target placement zone(s) is expected to belocated. There may be more than one target placement zone and one zonemay be preferred over another zone. At step 908, the system processesthe generated images and determines the desired target placement zone onthe trailer. The desired target placement zone may be determined basedon camera location and orientation, desired distance of the target fromthe hitch connection and the physical structure of the trailer. At step910, the system generates a target overlay on the one or more generatedimages. The target overlay is a visual indication of the desiredlocation of the target within the target placement zone upon which theuser is instructed to place the target. The target overlay may includeborder lines marking the target placement zone or other identifier. Thetarget overlay may be shown by flashing colored (e.g., red) lines on adisplayed image. Target overlays of a plurality target placement zonesmay be generated and shown. At step 912, the system communicates the oneor more images and the target overlay to the vehicle's display and ifconnected in step 902, the user's display on the portable device byutilizing the wireless or wired connection. Next, at step 914, theuser's display on the portable device displays an image of the targetplacement zone indicated by the target overlay. At step 916, the user isthen prompted by an HMI to place the target on the trailer within thetarget placement zone with assistance from the displayed image andtarget overlay on the vehicle's display and/or the portable display.

One example of a displayed image on the display 28 of a portable device26 showing an overlay of the target location for the target to be placedon the trailer is illustrated in FIG. 16. The image displayed on thedisplay 28 includes an image of the trailer 110 as captured by thecamera and further includes an overlay of the desired target placementzone 32. The user 2 may view the image on the display 28 of the portabledevice 28 to determine where to place the target relative to the trailer110. In this example, the user may place the target 30 onto the targetplacement zone 32 as indicated by the target overlay. Placement of thetarget may be achieved by adhering a target sticker onto a surface ofthe trailer. As a result, the user may employ a portable device with adisplay, such as a phone, a tablet, or a computer to view the properlocation for placement of the target on the trailer prior to and duringapplication of the target onto the trailer.

Accordingly, the target placement assist method 900 advantageouslyassists the user with placement of the target 30 onto the trailer 110 ina manner that is simple to use, accurate and efficient. The user 2 mayeasily transport a portable device having a display to communicate withthe vehicle and view the correct placement location for the target priorto and during the target placement procedure without having to return tothe vehicle or otherwise be prompted for target placement.

The trailer backup assist system 105 further includes a targetmonitoring method or routine for monitoring placement of the target onthe trailer and providing feedback to the user as to whether the targethas been placed within a proper target placement zone. A user may placea target on the trailer in various ways. In some situations, the usermay be prompted by the TBA system via a vehicle HMI to place a target onthe trailer and may be given instructions as to the location. The usermay employ the target placement assist method 900 to assist withplacement of the target on the trailer. In other situations, the usermay place the target on the trailer using their best judgment orfollowing instructions printed on the target or packaging providedtherewith. In any event, once the target is placed on the trailer, thetarget monitoring method 920 will monitor the location of the targetrelative to the trailer and provide feedback to the user as to corrector incorrect placement of the target on the trailer.

The target monitoring method 920 is illustrated in FIG. 18, according toone embodiment. At step 922, method 920 requires attaching the trailerto the vehicle onto the ball and hitch if it is not already attached.Next, at step 924, setup for the hitch angle detection is initiated. Atstep 926, the user is prompted via an interface to place the target onthe trailer. The user may place a target on the trailer based onpredefined criteria or the user's best judgment or knowledge, accordingto one embodiment. The user may be instructed on where to place thetarget on the trailer by use of a user's manual, an instruction sheet,or other visual or audible communication of instructions, according toother embodiments. Generally, the target should be placed in a regionthat is unobstructed from view by the camera and that allows for theacquisition of an image and determination of desired trailer relatedinformation, such as the hitch angle. Depending on the trailerconfiguration and camera orientation and height, the target may berequired to be placed within a certain region of the trailer, within adistance range from the trailer hitch connection having a minimumdistance from the hitch connection, such as 7 inches (17.78centimeters), within a range from the tow vehicle bumper, and within arange of height from the ground. The target placement may require alocation within a certain distance from a centerline of the longitudinalaxis of the trailer, and may require a vertical or horizontal angle orsome angle in between the vertical and horizontal positions. Accordingto another embodiment, the user may utilize the target placement assistmethod 900 to place the target on the trailer.

At step 928, the system generates one or more images of the targetplacement zone on the towed trailer. The system then processes the oneor more images to determine the presence of a target within a desiredtarget placement zone at step 930. The desired target placement zone maybe determined by criteria, such as distance from the trailer hitchconnection formed by the coupler assembly 114, distance from acenterline of the longitudinal axis of the trailer, height of the camerarelative to the trailer, and distance of the camera from the trailer. Atdecision step 932, method 900 determines if the target has been detectedby the processed image(s) and, if not, returns to step 926 to prompt theuser via an HMI to place the target on the trailer.

If the target has been detected by the processed images, the vehicletrailer backup assist system provides a feedback alert to the user atstep 934. The feedback alert may include one or more of vehicle exterioralerts including visual alerts, such as flashing the vehicle brakelights and/or flashing the vehicle emergency flashers, and/or audiblealerts, such as sounding the vehicle horn. Additionally, the feedbackalerts may include providing a message via the portable device 26,providing an audible tone via the portable device 26 or a visual lightedindication via the portable device 26. Further, feedback alerts mayinclude sending a text message or audible instructions to a user via aportable device, such as a phone or computer. It should be appreciatedthat other vehicle exterior and alternative feedback alerts may becommunicated to the user to indicate that proper placement of the targethas been detected on the trailer. Alternatively, the feedback alertscould be used to indicate improper placement of the target on thetrailer. Once the trailer is properly equipped with the target in theproper location, the trailer backup assist system may processinformation by monitoring the target to determine the hitch angle andother trailer towing related functionality.

The target 30 may include a sticker having adhesive on the bottomsurface and a predetermined image pattern of a certain size and shapeprovided on the top surface for capture by the video camera andrecognition by the image processing. The target 30 may have arectangular shape, according to one embodiment, and may have a cameraimage recognizable pattern such as the checker pattern shown. The imageprocessing may include known image pattern recognition routines foridentifying a target pattern and its location on a trailer. However, itshould be appreciated that other target shapes, sizes and patterns maybe employed. It should further be appreciated that the target mayotherwise be connected to the trailer using connectors, such asfasteners, which may connect to the trailer or to an attachment to thetrailer. It should further be appreciated that the target can beattached via magnet, glued on, painted on, or any number of othersuitable means.

It should be appreciated that not all trailers are necessarilyconfigured to provide a well-suited location for placement of a targetsticker on the trailer. Accordingly, a target location may be added to agiven trailer by use of a target mounting system 40 as shown in FIGS. 19and 20, according to one embodiment. The target mounting system 40 isshown installed onto trailer 110 to present a target 30 that is viewableby the camera within a desired target placement zone. The targetmounting system 40 includes a vertical mounting post or bracket 44having a plurality of bolt receiver holes 46 extending vertically toallow for a desired vertical height adjustment. The bracket 44 may beassembled onto the trailer via holes 54 using bolts 48, washers 52 andnuts 50. The height of the bracket 44 may be adjusted depending on whichholes 46 are aligned with the trailer holes 54. Mounted to the top ofthe bracket 44 is a target plate 42 having a top target placement zone32 onto which the target 30 is located. The plate 42 likewise has aplurality of holes 46 that align horizontally with the holes in thebracket 44 and may be assembled thereto via bolts 48, washers 52 andnuts 50. Accordingly, the plate 42 may be adjusted both vertically andhorizontally to a desired position so as place the target 30 adjustablywithin a desired location so that the target is easily acquired by thecamera and processed by the image processing. It should be appreciatedthat assistance in mounting the target mounting system 40 along with thetarget 30 and verification of proper location of the target mountingsystem 40 and target 30 may be achieved by utilizing the targetplacement assist method 900 and target monitoring method 920 discussedabove.

The target moved detection method includes an initial setup routine 940and subsequent processing routine 960 for target moved detection usedfor prompting the entry of trailer information. The target moveddetection method determines if the location of a hitch angle target on atrailer, such as a trailer tongue, has moved and may also determine ifthe distance has changed. Images of the target in a previously storedimage and a newly acquired image are compared to determine if thelocation and/or distance to the target has changed. The comparison mayinclude comparing camera image pixel sizes of the images. If either thelocation or the distance changes, the user is then prompted by an HMI toreenter new trailer information for subsequent processing of the trailerbackup assist system.

The initial setup routine 940 is illustrated in FIG. 21. Initially, thetrailer must be attached to the vehicle at step 942. At step 944, theattached trailer is setup for hitch angle tracking. For a vision-basedsystem, this may include applying a target sticker to the trailer, suchas in the vicinity of the tongue of the trailer, so that thevehicle-based camera can detect motion of the target as the trailermaneuvers and swings around curves. In addition, a number of parametersassociated with the location of the target that are used to properlycalculate the hitch angle based on the vision processing may be entered.These parameters may include the distance of the target to the groundand the distance from the target to the bumper of the vehicle. At step946, the vehicle and the trailer are directed to be driven straight,which may be achieved by driving the vehicle and towed trailer in theforward direction. This is to ensure that there is about zero hitchangle between the vehicle and trailer with the trailer in-line with thevehicle and that the image generated in subsequent steps will be takenin the same orientation and will be valid for image comparisons. At step948, a picture (image) of the target and trailer are acquired with theuse of the camera while the vehicle and the trailer are in a straightline at a hitch angle of about zero degrees. At step 950, the imageprocessing performs vision processing on the image. The visionprocessing may first detect a target and then compute the size andlocation of the target based on processing the pixels of the image. Atstep 952, the image acquired in step 948 is stored in memory and theinformation calculated in step 950 is stored in memory. The image andcalculated information are then subsequently used to determine if thetarget has moved. If the target has moved, the system may assume thatthe trailer may have been changed or replaced with a different trailer,and hence prompts the user via an HMI to enter trailer information.

Referring to FIG. 22, the target moved detection routine 960 is shownbeginning at step 962 in which the driver is instructed to reattach tothe vehicle a trailer that was previously set up and used in the initialsetup routine 940. At step 964, the user is prompted by the hitch angledetection system to select the trailer that was previously setup andstored, rather than selecting a new trailer. At step 966, the user isprompted to drive the trailer and vehicle combination forward in astraight line to achieve a hitch angle of about zero degrees. Next, atstep 968, a new image of the target and the trailer are acquired by thecamera. At step 970, vision processing is performed on the image todetect the target and compute the size and location of the target byprocessing the pixels of the image. At step 972, the target location andsize as calculated above are compared to the location and size of thetarget taken in the prior image from the initial setup. At step 974, adetermination is made to determine if the new target information is amatch or within tolerance of the original target information. If thenewly acquired target is still a similar size and in the similarlocation on the image as compared to the prior image from the initialsetup, then the target is likely to be in the same location and willallow for a proper hitch angle detection if determination of such ismade in step 980. If the target has a different location or has adifferent size, then the target is presumed to have moved and routine960 proceeds to step 976. Detected movement of the target may occur whenthe trailer is a different trailer as compared to the trailer lastselected by the user. The use of the prior selected trailerconfiguration may provide erroneous results for hitch angle targettracking. As such, method 960 proceeds to step 978 to prompt the user(e.g., driver) to reselect or re-setup the trailer configuration withnew target and trailer information. Accordingly, the target moveddetection routine 960 advantageously detects movement of the targetwhich may indicate potential connection of a new trailer to the vehicle,such that the user is prompted via an HMI to select new trailerconfiguration information. Additionally, the target moved routine couldalso detect that a target has moved due to a different sized drawbarbeing installed than what was installed when the trailer was initiallysetup.

Examples of images of the trailer and the target moved to a differentposition are illustrated in FIGS. 23A and 23B. As shown in FIG. 23A, animage of the trailer and the target 30 is shown aligned on the trailerin a first position as compared to the subsequent image in FIG. 23Bshowing the target 30 moved to a new second closer position. The changein location of the target may be an indication that the trailer has beenchanged out with a new trailer or that the target has otherwise beenmoved on the trailer. When this occurs, the target move detectionroutine 960 requires the user to re-enter trailer configurationinformation so that the wrong information is not used to provideincorrect hitch angle data. Furthermore, it is possible that the right(correct) trailer has been selected and the target is still in the samelocation on the trailer, but the system still indicates that the targethas moved. This could occur if the drawbar length on the vehicle haschanged.

Target monitor controller 10 further processes a trailer connectionmonitoring routine 990 to determine whether a trailer is connected tothe vehicle and whether a new trailer may have been connected. When thetrailer is disconnected from the vehicle, the target information and thehitch angle information may be unavailable for a period of time.Accordingly, the trailer connection monitoring method 990 monitors theavailability of the hitch angle data and/or the detection of the targetto determine if the hitch angle data or target data is lost for asubstantial period of time. If this occurs, the driver is then promptedvia an HMI to reselect the attached trailer or to re-enter trailerconfiguration data to ensure that the wrong trailer information is notemployed.

The trailer connection monitoring routine 990 is illustrated in FIG. 24.At step 992, a trailer is connected to the vehicle. At step 994, thetrailer is setup for hitch angle detection and monitoring. If a visionbased system is employed, this may include placing a target on thetrailer for the vision-based system to detect as well as enteringpertinent parameters. Alternatively, if the trailer has been previouslysetup for hitch angle monitoring, it may be possible to select thepreviously stored setup configuration for that trailer. At step 996,once the trailer has been setup for hitch angle detection, the hitchangle detection system will continuously monitor the hitch angle ortarget. At decision step 998, routine 990 determines if the hitch angleor the target has been dropped for a time period greater than X seconds.

Depending on the type of hitch angle system, the hitch angle signal maydrop or become unavailable for different reason, but one potentialreason is that the trailer has been disconnected from the vehicle. Adisconnected trailer may also result in the target detection beingunavailable. As such, a check is made to see how much time has expiredsince the hitch angle signal or target detected has been dropped. If thehitch angle or target detection has been dropped for a time period ofless than X seconds, then routine 990 returns to track the hitch angleor target at step 996. If the hitch angle or target detection has beendropped for a time period greater than X seconds, then the user isprompted via an HMI to reselect or re-setup the trailer configuration instep 1000. The time period X is set to represent a reasonable amount oftime needed to swap or change-out trailers. For example, for extremelysmall, lightweight trailers, it may be possible to swap trailers out inless than sixty (60) seconds, so this could be a reasonable time period.According to one embodiment, the time period X is set for thirty (30)seconds.

While the hitch angle is monitored to determine disconnection of atrailer from the vehicle, it should be appreciated that the trailerconnection monitoring routine 990 may monitor detection of the target asan alternative, such that if the target is no longer detected for Xseconds, then the vehicle driver may be prompted to reselect orreconfigure the trailer.

Supplemental Vehicle Lighting System

As previously described, the trailer backup assist system 105 may employa vision based target detection system, wherein the hitch angledetection component 155 is an identifiable visual target located on atrailer attached to a towing vehicle. The towing vehicle may be equippedwith a rear view camera, which functions as the hitch angle detectionapparatus 130, and is configured to image the target and processacquired image data to generate trailer related information used in avariety of applications associated with the trailer backup assist system105. By following the previously described target placement assistmethod 900 and/or other suitable methods, a vision based targetdetection system can be readily configured for accurate targetdetection. Nevertheless, there may be some circumstances that hindertarget detection accuracy. One such circumstance involves performingtarget detection under dark conditions when existing vehicle lights,such as taillights, provide insufficient target lighting. Whileaftermarket lighting assemblies are available, such assemblies mayappear unsightly and may lack the ability to be integrated with thetrailer backup assist system 105. Thus, it is desired to provide asupplemental vehicle lighting system that not only cooperates with thetrailer backup assist system 105, but also confers a styling advantageto vehicles in which it is featured.

As will be described in greater detail below, a supplemental vehiclelighting system is disclosed herein that utilizes an existing keylockhole of a rear vehicle closure member or other rear vehicle fixture. Forpurposes of illustration, FIG. 25A exemplarily shows a tow vehicle 1005having a rear vehicle closure member embodied as a tailgate 1010 thatincludes a keylock hole 1015 defined in a tailgate handle assembly 1020.As exemplarily shown in FIGS. 25B-25D, the keylock hole 1015 iscustomarily used in conjunction with a corresponding keylock cylinder1025 that includes a keyhole 1030 that is accessible through the keylockhole 1015. It should be appreciated that the keylock cylinder 1025 maybe supported inside the tailgate 1010 in a variety of ways. For purposesof illustration, the keylock cylinder 1025 is shown engaged toprotrusions 1035, 1038, and 1040 of the tailgate handle assembly 1020and is secured to the tailgate handle assembly 1020 with mechanicalfastener 1045. When a corresponding key is inserted into the keyhole1030 and turned in the proper direction, a locking tab 1050 of thekeylock cylinder 1025 is moved to an unlocked position to enable thetailgate 1010 to be lowered so that a rear vehicle cargo area can beaccessed. While the rear closure member has been generally describedherein as a tailgate 1010, it should be appreciated that the rearclosure member may also include a liftgate, a trunk lid, a swing door, asliding door, and the like, depending on the type and/or make of theselected vehicle 1005. Likewise, it should also be appreciated that theconfiguration and/or location of the keylock hole 1015 and keylockcylinder 1025 may vary across vehicle types and/or makes. Therefore, thekeylock hole 1015 may be defined in other parts and/or areas of the rearvehicle closure member or in some other rear vehicle fixture altogether.

While many current vehicles are equipped with a keylock hole and akeylock cylinder, seldom is a key used to unlock a rear vehicle closuremember given the proliferation of vehicles having power lock systems orother means of entry. Thus, with respect to some vehicles, the inclusionof a keylock cylinder produces added cost and consumes space that couldotherwise be used to implement other devices. Recognizing this, asupplemental vehicle lighting system is provided herein thatadvantageously replaces a keylock cylinder with a light assemblyoperably coupled to a rear keylock hole of a selected vehicle, throughwhich the light assembly is able to illuminate a rear vehicle area. Inso doing, little to no modification need be made to existing rearvehicle fixtures since the light assembly may be fashioned to be mountedto in the same way as the keylock cylinder. In this manner, vehiclemanufacturers can offer vehicles equipped with a light assembly withouthaving to perform substantial retooling. Similarly, an existing keylockcylinder may be easily swapped for a light assembly in vehicles desiringthe benefits bestowed by the supplemental vehicle lighting systemdescribed herein.

Referring to FIGS. 26A-26D, a light assembly 1055 is shown according toone embodiment and includes a housing 1060 having an open top defined byan upper edge 1065. The light assembly 1055 also includes a barrel 1070having a distal end 1075 and a proximal end 1080. A lighting device 1085including one or more light emitting diodes (LEDs) 1087 is disposedinside the housing 1060 and is configured to emit light through thebarrel 1070 beginning from the proximal end 1080. The barrel 1070 may beconstructed from a reflective material to trap the emitted light insidethe barrel 1070 as it propagates towards the distal end 1075 of thebarrel 1070. The emitted light is then dispersed from the barrel 1070via a lens 1090 that is coupled to the distal end 1075 of the barrel1070.

In the illustrated embodiment, the lens 1090 includes a first section1091, a second section 1092, and an intermediate section 1093therebetween. The second section 1092 is configured to be inserted intothe barrel 1070 through the distal end 1075 such that the intermediatesection 1093 abuts against the distal end 1075 and may be adheredthereto using an adhesive. In this arrangement, the first section 1091is most distal to the lighting device 1085. Additionally, the firstsection 1091 may be curved and optically configured to disperse theemitted light in a variety of directions including a forward, upward,downward, and/or sideways direction.

As best shown in FIGS. 26C and 26D, the lighting device 1085 has anL-shaped configuration and is electrically coupled to an electricalconnector 1095 provided at the bottom of the housing 1060. The lightingdevice 1085 includes a first end 1097 that abuts against the proximalend 1080 of the barrel 1070 and supports a heat sink board 1100 on whichthe LEDs 1087 are mounted. The lighting device 1085 also includes a plug1102 disposed at a second end having pins 1107 that plug into acorresponding socket 1109 of the electrical connector 1095. To supplypower to the lighting device 1085, the electrical connector 1095 may beconfigured to make an electrical connection with an onboard vehiclepower source or other power source.

To assist the heat sink board 1100 with heat dissipation, the lightassembly 1055 may include a heat management member 1115 positionedproximate to the lighting device 1085. The heat management member 1115may be a straight heat sink (as shown), or other heat sink type, suchas, but not limited to, a pinned heat sink or a flared heat sink, andmay be mounted to the upper edge 1065 of the housing 1060 via threadedfasteners 1120. Optionally, a thin plate 1122 may be provided fordistributing the load of the threaded fasteners 1120. As shown in FIG.26C, the thin plate 1122 is contiguous with the upper edge 1065 of thehousing 1060 and is disposed between the upper edge 1065 of the housing1060 and the heat management member 1115.

Referring to FIGS. 27A and 27B, the light assembly 1055 is exemplarilyshown mounted to the tailgate handle assembly 1020 previously shown inFIGS. 25A-25D. The light assembly 1055 is configured to be engaged toprotrusions 1035, 1038, and 1040 and is secured to the tailgate handleassembly 1020 with mechanical fastener 1045 to mirror the mountingscheme of the keylock cylinder 1025 previously shown in FIG. 25D. Inthis manner, the keylock cylinder 1025 and light assembly 1055 areeasily interchanged. However, it should be appreciated that othermounting schemes may be employed for mounting the light assembly 1055 tothe tailgate handle assembly 1020 or other rear vehicle fixture. Withrespect to the presently illustrated embodiment, mounting of the lightassembly 1055 to the tailgate handle assembly 1020 results in theintermediate section 1093 of the lens 1090 abutting against an interiorsurface 1125 of the tailgate handle assembly 1020. In this arrangement,the barrel 1070 is concentrically aligned with the keylock hole 1015such that the first section 1091 of the lens 1090 at least partiallycoincides with the keylock hole 1015 while the tailgate handle assembly1020 shields the rest of the light assembly 1055. Once the lightassembly 1055 is secured, an electrical connection may be made betweenthe electrical connector 1095 of the light assembly 1055 and a plug 1127stemming from an onboard vehicle power supply or other power source suchthat power may be supplied to the lighting device 1085.

In operation, the lighting device 1085 may be activated using a varietyof means. For example, the lighting device 1085 may be manuallyactivated via a user input mechanism, such as a button located on ahuman machine interface (e.g. HMI 102), or elsewhere in the selectedvehicle. Additionally, or alternatively, the lighting device 1085 may beautomatically activated via an onboard vehicle system such as thetrailer backup assist system 105 and/or other vehicle system. Forinstance, when performing a backup maneuver, the trailer backup assistsystem 105 may activate the lighting device 1085 under dark conditions.In another instance, the lighting device 1085 may be automaticallyactivated during set up of the trailer backup assist system 105, asdescribed previously in step 604 of FIG. 10.

Referring to FIG. 28, a supplemental vehicle lighting system 1130 isimplemented in the vehicle 1005 previously shown in FIG. 25A. Forpurposes of illustration, the vehicle 1005 features the trailer backupassist system 105 and employs vision based target detection. As shown,the vehicle 1005 is attached to a trailer 1135, which may be variouslyconfigured and may offer one or more suitable target placement zones forreceiving a target 1140. In the illustrated embodiment, the target 1140is placed on a trailer tongue 1145 of the trailer 1135 and is imaged bya rear view camera 1150 mounted in an upper region of the tailgate 1010.By virtue of its positioning in the tailgate 1010, the rear view camera1150 is shown imaging a scene 1155 that is to the rear of the vehicle1005 and points slightly downwards therefrom so that the target 1140 ispresent in the scene 1155. To assist the camera 1150 in accuratelyimaging the target 1140 in dark conditions, the light assembly 1055described previously herein is mounted inside the tailgate 1010 and isoperable to illuminate a rear vehicle area 1160 that includes the target1140 and at least partially overlaps with scene 1155. With respect tothe illustrated embodiment, it can be seen that the rear vehicle area1160 can include the area behind a rear bumper 1165 of the vehicle 1005.Since the keylock hole 1015 is defined in the tailgate handle assembly1020, the light assembly 1055 may be mounted to the tailgate handleassembly 1020 in the manner described in reference to FIG. 27A or othersuitable manner.

Although the supplemental vehicle lighting system 1130 has beendescribed herein as being featured in a tow vehicle 1005 generallyembodied as a pickup truck, it should be appreciated that thesupplemental vehicle lighting system 1130 may be featured in other towand non-tow vehicles alike, which may include, but are not limited to,buses, sports utility vehicles, vans, station wagons, sedans, andcoupes. Furthermore, while the supplemental vehicle lighting system 1130is intended for use with the trailer backup assist system 105, it shouldbe appreciated that the vehicle lighting system 1130 may additionally,or alternatively, be adapted for use with other vehicle relatedapplications. For example, the additional lighting provided by the lightassembly 1055 will enable a vehicle equipped with a rear view camerasystem to render clearer images on a display screen when it's darkoutside. This may prove especially useful when performing a backupmaneuver in low visibility situations. At the most basic level, thesupplemental vehicle lighting system 1130 may simply be used as autility light. For example, the light assembly 1055 may be activated toaid an operator with attaching/detaching a trailer to/from a tow vehiclein low light conditions.

Secondary Hitch Angle Sensor System

For the trailer backup assist system 105, as previously described, it isadvantageous to use information that is representative of an anglebetween the vehicle and a trailer attached to the vehicle, also known asthe hitch angle γ or trailer angle. In addition to the trailer backupassist system 105, it is contemplated that other vehicle systems mayutilize hitch angle information as an input to the system, whereby thehitch angle information may be manipulated by a controller ormicroprocessor associated with the vehicle 100. In some embodiments, ameasured hitch angle γ(m) may not provide an accurate measurement of theactual hitch angle γ(a) to a requesting system, which may introduce apotential for inadequate or improper vehicle system control, especiallyin situations where the hitch angle information may be important to thevehicle system being controlled, such as the trailer backup assistsystem 105. Furthermore, as previous mentioned, the hitch angle signalmay drop-out or become unavailable for different reasons, such as thehitch angle detection apparatus 130 momentarily being unable to sensethe relative position of trailer 110, or more specifically, the camera20 being unable to track the hitch angle target 30 or other hitchsensors, such as a potentiometer, magnetic, optical, or mechanical basedsensors, being unable to provide a constant hitch angle measurement,which may similarly cause errors or other disruption in operating thetrailer backup assist system 105. Accordingly, an accurate andconsistent estimate of the actual hitch angle γ(a) is desired, includingfor a means to confirm the accuracy of a measured hitch angle γ(m).

Referring to FIGS. 29-31, a sensor system 1200 for estimating a hitchangle of a trailer 110 attached to a vehicle 100 is shown according toone embodiment, which includes a primary sensor 1202 having a camera 20monitoring a target 30 on the trailer 110 to determine a measured hitchangle γ(m) and a secondary sensor 1204 that monitors the trailer 110 todetermine an indicator 1206 of the actual hitch angle γ(a). In thisembodiment, the trailer backup assist system 105 operates the vehicle100 when the measured hitch angle γ(m) correlates with the indicator1206 of the actual hitch angle γ(a). This and other embodiments of thesensor system 1200 are described in more detail below.

In the embodiment illustrated in FIG. 29, the vehicle 100 is a pickuptruck that employs vision based target detection as the primary sensor1202 to determine the measured hitch angle γ(m). Accordingly, theprimary sensor 1202 on the vehicle 100 includes a hitch angle detectionapparatus 130 that has a camera 20 as an input for providing videoimages to a target monitor controller 10 of the primary sensor 1202. Thecamera 20 (e.g. video imaging camera) is located proximate an upperregion of the vehicle tailgate at the rear of the vehicle 100, such thatthe camera 20 is elevated relative to the target placement zone(s) andhas an imaging field of view located and oriented to capture one or moreimages of the trailer 110, including a region containing one or moredesired target placement zone(s) 32. It should be appreciated that thecamera 20 may include one or more video imaging cameras and may belocated at other locations on the vehicle 100 to acquire images of thetrailer 110 and the desired target placement zone(s) 32.

As also shown in FIG. 29, the tow vehicle 100 is pivotally attached toone embodiment of a trailer 110. The trailer 110 has a trailer hitchconnector in the form of a coupler assembly 114 connected to a vehiclehitch connector in the form of a receiver hitch and ball 15. The couplerassembly 114 latches onto the hitch ball 15 to provide a pivoting balljoint connection 117. The trailer 110 is shown having a frame 1208 thatincludes a longitudinally extending bar or trailer tongue 112 that iscoupled with opposing front frame members 1210 that angle laterally awayfrom the trailer tongue 112 and extend rearward to couple with sideframe members 1212 that extend longitudinally in parallel alignment andare supported by a rotatable wheel axle 1214 of the trailer 110. Theforward facing surfaces of the trailer frame 1208, including the trailertongue 112 and the front and side frame members, 1210, 1212 providesurfaces for the secondary sensor 1204 to monitor the position of thetrailer 110. Again, it should be appreciated that the trailer 110 may beconfigured in various shapes and sizes, may include more than one axle,and may have additional or alternative surfaces for the secondary sensor1204 (FIG. 30) to monitor.

With further reference to FIG. 29, the vehicle 100 has additionalonboard proximity sensors, including but not limited to, a reverse aidsystem 1220, a blind spot system 1216, and a cross traffic alert system1218. In one embodiment, the reverse aid system 1220 includes a pair ofenergy transducers coupled with the rear of the vehicle 100 below thevehicle tailgate on opposing sides of the pivoting ball joint connection117 between the vehicle 100 and the trailer 110. The energy transducersof the reverse aid system 1220, in the illustrated embodiment, compriseultrasonic sensors that are directed rearward in the general vicinity ofthe trailer 110 for monitoring the position of the trailer 110 bymeasuring a difference in return signals from the ultrasonic sensors onopposing sides of the pivoting ball joint connection 117. The differencein the return signals is used to determine the indicator 1206 (FIG. 30)of the actual hitch angle γ(a). The indicator 1206 may be a secondmeasured hitch angle γ(m2), which can be used to define an acceptabletolerance range of hitch angles. The indicator 1206 may also be anotherconceivable type of indicator, as described in further detail herein.The reverse aid system 1220 may include additional sensors, includingother types of sensors, such as radar sensors, located at severallocations at the rear of the vehicle 100, such as laterally spaced alongthe bumper.

The blind spot system 1216, according to one embodiment shown in FIG.29, includes an energy transducer 1222 coupled with each of the siderear view mirrors that generate a sensor field adjacent to the sides ofthe vehicle 100 and rearward therefrom in the general vicinity of thetrailer 110. The energy transducers 1222 of the blind spot system 1216may be ultrasonic sensors that monitor the general position of thetrailer 110 to determine an indicator 1206 of the actual hitch angleγ(a). Accordingly, it is conceivable that the blind spot system 1216 maybe used to determine when the trailer 110 is roughly centered behind thevehicle 100 or in line with the vehicle 100 when the return signals fromboth energy transducers 1222 are both low and/or relatively equal. Also,the blind spot system 1216 may provide an indicator 1206 (FIG. 30) ofthe actual hitch angle γ(a) based on the magnitude of return signal fromthe respective energy transducer 1222 receiving the greater returnsignal. For instance, a set of ranges of ascending magnitudes may be setto correspond with a general hitch angle (e.g. 10-20 Hz for 5 degrees,20-30 Hz for 10 degrees, etc.) or ranges of hitch angles (e.g. 0-40degrees, 40-70 degrees, 70-100 degrees), such that the return signal maybe an indicator 1206 (FIG. 30) of the actual hitch angle γ(a) for usewith the sensor system 1200 or for use as a primary sensor 1202 in analternative embodiment.

The cross traffic alert system 1218, as shown in FIG. 29, alsoincorporates energy transducers 1224 on the rear of the vehicle 100 togenerate sensor fields for monitoring the general position of thetrailer. Specifically, the cross traffic alert system 1218 in theillustrated embodiment includes energy transducers 1224 comprising apair of ultrasonic sensors directed rearward and laterally outward fromthe rear of the vehicle 100, such that the ultrasonic sensors maydetermine when the trailer 110 has reached a large hitch angle or isapproaching a critical angle indicative of a jackknife condition orjackknife angle γ(j). In addition, the secondary sensor 1204 maycomprise an auxiliary hitch angle sensor 1226 (FIG. 30) attached to thetrailer 110 and/or the vehicle 100, such as mechanical sensor mechanismsor other conceivable hitch angle sensors. It is also contemplated thatany of the onboard proximity sensors (FIG. 32), including, but notlimited to, the reverse aid system 1220, blind spot system 1216, thecross traffic alert system 1218, and the auxiliary sensor 1226, may havean ultrasonic sensor, a radar sensor, or a combination of the two. Thesesecondary sensors 1204 for determining the position of the trailer 30may also include other cameras located on the vehicle, cameras locatedon the trailer, or other sensing devices generally understood by onehaving ordinary skill in the art. It is also conceivable that more thanone onboard sensor system may be incorporated into the secondary sensor1204, offering multiple individual sensors that contribute to theindicator 1206 of the actual hitch angle γ(a).

Referring to FIG. 30, the sensor system 1200 of the trailer backupassist system 105 (FIG. 1) has the primary sensor 1202 for determining afirst measured hitch angle γ(m) and the secondary sensor 1204 fordetermining an indicator 1206 of the actual hitch angle γ(a), such as asecond measured hitch angle γ(m2). In one embodiment, the secondarysensor 1204 may be used in place of the primary sensor 1202 when thesignal of the first measured hitch angle γ(m) becomes unavailable orunreliable, thereby using the second measured hitch angle γ(m2) in placeof the first measured hitch angle γ(m). Additionally or alternatively,the secondary sensor 1204 may be used in conjunction with the primarysensor 1202 to confirm that the first measured hitch angle γ(m)correlates with the indicator 1206 of the actual hitch angle γ(a). Inone embodiment, as described above, the primary sensor 1202 may includethe hitch angle detection apparatus 130 and the target monitorcontroller 10 for monitoring the target 30 on trailer 110 to determinethe first measured hitch angle γ(m). The secondary sensor 1204 includesa trailer monitoring apparatus 1228 and a trailer monitoring controller1230 for monitoring the trailer 110 to determine the indicator 1206 ofthe actual hitch angle γ(a). The trailer monitoring controller 1230 mayinclude a microprocessor 1232 and/or other analog and/or digitalcircuitry for processing one or more routines. Also, the trailermonitoring controller 1230 may include memory 1234 for storing one ormore routines including sensor signal processing routines 1236 and hitchangle confirmation routines 1238. It should be appreciated that thetrailer monitoring controller 1230 may be a standalone dedicatedcontroller or may be a shared controller integrated with other controlfunctions, such as integrated with the trailer monitoring apparatus 1228and/or the primary sensor 1202, to process the return signals of theonboard proximity sensors or other secondary sensors and perform relatedfunctionality.

The trailer monitoring controller 1230 illustrated in FIG. 30 receivesand processes return signals from at least one of the camera 20, theblind spot system 1216, the reverse aid system 1220, the cross trafficalert system 1218, and the auxiliary hitch angle sensor 1226, which mayinclude additional processing from the trailer monitoring apparatus1228. The secondary sensor 1204 processes the return signals todetermine the indicator 1206 of the actual hitch angle γ(a), such asusing the reverse aid system 1220 to determine a second measured hitchangle γ(m2) as the indicator 1206 and/or using the blind spot system1216 to determine a range of hitch angles as the indicator 1206. Thehitch angle confirmation routine 1238 further processes the indicator1206 in connection with the first measured hitch angle γ(m) to determineif the first measured hitch angle γ(m) correlates with the indicator1206. For instance, the indicator 1206 may include the second measuredhitch angle γ(m2) that defines a tolerance range of acceptable hitchangles (e.g. +/−3 degrees of the second measured hitch angle, or a wideror narrower tolerance range), such that the first measured hitch angleγ(m) correlates with the indicator 1206 when the first measured hitchangle γ(m) is within the tolerance range. It is contemplated that in oneexemplary embodiment, the hitch angle confirmation routine 1238 may alsoprocess the first measured hitch angle γ(m) to define an averagemeasurement thereof over an interval of time (e.g. 2 seconds, or alonger or shorter interval) to reduce instability and variance of thefirst measured hitch angle γ(m).

As also illustrated in FIG. 30, the sensor system 1200 may communicatewith one or more devices including, the vehicle HMI 25, the vehicleexterior alerts 24, and the vehicle interior alerts 1240, which mayinclude a blind spot indicator light 1242 that provides a visual alert.It is contemplated that the blind spot indicator light 1242 may be on aninterior or exterior of the vehicle 100, such as on or proximate a siderear view mirror, to alert the driver that the primary sensor 1202 doesnot correlate with the indicator 1206 of the actual hitch angle γ(a),the trailer 110 is approaching or is in a jackknife condition, or otherconceivable warnings that may not be able to be displayed on the centerstack screen when reversing the vehicle 100. Additional warnings thatmay be provided with the blind spot indicator light 1242 includeoverspeed warning that alerts the driver that they are approaching aspeed greater than the speed configured for operating the trailer backupassist system 105, a steering override warning that alerts the driverthat steering has exceeded the acceptable steering torque configured foroperating the trailer backup assist system 105, or an internal faultwarning that alerts the driver that the trailer backup assist system 105has become inoperative and has to canceled out for other conceivableerrors. As previously described, the sensor system 1200 may communicatevia wireless communication 22 to various types of mobile devices or viaonboard communication to one or more vehicle human machine interfaces(HMIs) 25, including a vehicle display, such as a center stack mountednavigation/entertainment display.

The method for estimating the actual hitch angle γ(a) using the sensorsystem 1200 of the trailer backup assist system 105 is illustrated inFIG. 31 according to one embodiment. Initially, at step 202 the systemmay receive an initiation request to activate the trailer backup assistsystem 105 for tracking the hitch angle. Before proceeding to monitorthe hitch angle, at step 1244 the system confirms that the attachedtrailer 110 has been calibrated and setup for operation with the trailerbackup assist system 105, and if not, the calibration and setup process600, 700 are initiated, as previously described. Although thecalibration and setup processes 600, 700 may involve gathering thekinematic information for the attached trailer 110, at step 1246, thesensor system receives this information for use with the primary and/orsecondary sensors 1202, 1204, if necessary. For instance, if a visionbased target detection system is included as the primary sensor 1202,the kinematic information will provide parameters from the target setupinformation in addition to the input or otherwise determined dimensionsof the trailer 110. The trailer kinematic information may also be usedby the sensor system 1200 to modify the tolerance range of acceptablefirst measured hitch angles and to modify the magnitudes of sensorreturn signals or corresponding ranges of hitch angles.

Still referring to FIG. 31, once the trailer backup assist system 105 isgenerally setup and calibrated with the trailer 110 attached to thevehicle 100, at step 1248, an input is made with the input device, suchas selecting the desired hitch angle between the vehicle 100 and trailer110 by manipulating the steering input apparatus 125, as previouslydescribed. At step 1250, the sensor system 1200 begins to monitor thetrailer 110 with the primary sensor 1202 to determine the first measuredhitch angle γ(m) at step 1252. In conjunction with the operation of theprimary sensor, at step 1254, the secondary sensor similarly monitorsthe trailer 110 to determine the indicator 1206 of the actual hitchangle γ(a) at step 1256. At step 1258, the first measured hitch angleγ(m) is compared with the indicator 1206 to determine if the measuredhitch angle γ(m) of the primary sensor 1202 correlates therewith, and ifso, thereby reflecting a generally accurate measurement of the actualhitch angle γ(a). If the measured hitch angle γ(m) is determined to notcorrelate with the indicator 1206, the user may be prompted at step1260, such as being alerted with any of the interior or exterior alerts1240, 24, being alerted and/or requested with the vehicle HMI to directwhether the trailer backup assist system 105 should proceed to operatethe vehicle 100, and similarly being alerted and/or prompted with amobile device via wireless communication 22, as described above. If themeasured hitch angle γ(m) of the primary sensor 1202 correlates with theindicator 1206 of the actual hitch angle γ(a), then, at step 1262, thetrailer backup assist system 105 may operate to achieve the desiredinput made with the input device, such as steering the vehicle 100 withthe power-steering assist system 115 to achieve the desired hitch angleinput with the steering input apparatus 125.

While the illustrated embodiment of the sensor system 1200 includes aprimary sensor 1202 and a secondary sensor 1204, it should beappreciated that the sensor system 1200 may include addition sensors(tertiary sensor, quaternary sensor, etc.) with additional correspondingindicators for confirming the accuracy of the indicator 1206 from thesecondary sensor 1204 and the measured angle γ(m) from the primarysensor 1202. It is also be understood that the sensor system 1200 mayadditionally, or alternatively, be adapted for use with other vehiclerelated applications, such as trailer sway limiters or other conceivableapplications relying upon the accuracy of the measured hitch angle γ(m).

Hitch Angle Estimation and Verification

According to an additional embodiment for estimating the actual hitchangle, a system uses an estimated distance between a wireless receiveron the vehicle and a wireless transmitter on the trailer. The wirelessreceiver on the vehicle is located at a predetermined distance from atrailer mount and the wireless transmitter on the trailer is located atan end of the trailer opposite the trailer mount. With respect to thisembodiment, the system includes a controller for monitoring powerreturns of a signal transmitted from the transmitter to the receiver andfor estimating the distance between the transmitter and the receiver asa function of a path loss propagation of the transmitted signal. Theactual hitch angle is then estimated using the estimated distance, thepredetermined distance, and a trailer length.

Referring now to FIGS. 32-34, one embodiment the system for estimatingthe actual hitch angle is shown to include a wireless receiver 1270 on avehicle 100 with a trailer backup assist system 105. The wirelessreceiver 1270 is mounted at a known vehicle location, such as a centralvehicle body position. In the illustrated embodiment, the vehicle 100also has a controller 1272 for receiving information from the wirelessreceiver 1270, which may be a single centralized vehicle controller or acombination of controllers. The controller 1272 may be programmed toperform various functions and control various outputs and may have amemory 1274 associated therewith. The memory 1274 may store variousparameters, thresholds, patterns, tables, or maps; for example,parameters may include known, fixed vehicle measurements such as wheelbase, vehicle length, trailer length and distances from known parts ofthe vehicle. The controller 1272 receives information from a number ofsensors on or around the vehicle 100 associated with one or more sensingsystems 1276, which may include, but are not limited to, speed sensors,yaw rate sensor, lateral acceleration sensor, roll rate sensor, verticalacceleration sensor, a longitudinal acceleration sensor, a pitch ratesensor, and a steering angle position sensor. These sensors may also bepart of an inertial measurement unit that would most likely be locatedat the center of the vehicle body.

As shown in FIGS. 32-33, a trailer 110 may be towed behind the vehicle100. The trailer 110 may include a tongue 112 and trailer wheels, aswell as a trailer brake and electrical components such as lights. Awiring harness 1278 may be used to couple the trailer 110 to theelectrical system of the vehicle 100 and ultimately to the controller1272. The trailer 110 is coupled to the vehicle 100, as by a hitch ball15 or other mount on the vehicle 100, through a coupler assembly 114located at the end of the trailer tongue 112. A distance d_(r) defines areference distance which is the distance between the wireless receiver1270 on the vehicle 100 and the hitch ball 15 or other mount on thevehicle 100. This is a fixed distance and may be stored in memory 1274.The coupler assembly 114 may have a hitch angle sensor 1226 associatedtherewith. Alternatively, the hitch angle sensor 1226 may be associatedwith the mount on the vehicle 100. The hitch angle sensor 1226 is usedto determine the angle position of the trailer 110 relative to thevehicle 100. Various types of hitch angle sensors, such as resistive,inductive, ultrasonic, or capacitive type sensors may be used, inaddition to other hitch angle sensor system disclosed herein.

A wireless transmitter 1280 is positioned on the trailer 110 at a knownlocation, preferably at the end of the trailer. This wirelesstransmitter 1280 is in communication with the wireless receiver 1270that is located on the vehicle 100. The wireless receiver 1270 has beenplaced at a known location of the vehicle 100 such that a referencedistance, d_(r), from the receiver 1270 to the hitch ball 15 at the rearof the vehicle 100 is known and stored in memory 1274. Examples ofwireless transmitting and receiving devices that may be used are RadioFrequency Identification (RFID), Bluetooth, and the like. As discussedabove, the wireless receiver 1270 is positioned at a location on thevehicle 100 the predetermined distance, d_(r), from the vehicle'strailer mount or hitch ball 15. The wireless transmitter 1280 and thewireless receiver 1270 are compatible units that transmit and receivesignals between the vehicle 100 and the trailer 110. The controller 1272monitors the power returns of the transmitted signals. By monitoring thepower returns of signals sent by the transmitter to the receiver, thecontroller 1272 may estimate a distance, d, between the vehicle 100 andthe trailer 110.

The disclosed subject matter also uses a trailer length, l_(T). Thisvalue may be a known value entered by the driver, stored in controllermemory, or otherwise sensed, calculated or estimated. For example, anaccurate estimate of trailer length, l_(T), is possible usingmeasurements of the signal transmitted from the wireless transmitter1280 on the trailer 110 to the wireless receiver 1270 on the vehicle 100when the hitch angle is zero. It is also possible to estimate thetrailer length when the measurements are taken while the vehicle yawrate is zero for a predetermined period of time.

The hitch angle is thereby estimated using the trailer length, l_(T),and path loss propagation of a signal transmitted from the transmitteron the trailer 110 to the receiver 1270 on the vehicle 100. The hitchangle estimate may then be used as an input for control algorithmsassociated with a variety of vehicle systems 1281 such as trailer sway,trailer backup assist, stability control and other systems.Alternatively, the hitch angle estimate may be used to verify, orvalidate, the measurement taken by a hitch angle sensor.

Referring to FIG. 33, a block diagram of a vehicle 100 and trailer 110combination, where a hitch angle is non-zero, is shown with respect tothe law of cosines:

A ² =B ² +C ²−2BC cos(a)

The vehicle 100 has the trailer 110 attached thereto with the receiver1270 located on the vehicle a predetermined reference distance, d_(r)from the trailer hitch ball 15, which corresponds to B for the trianglereflecting the law of cosines in FIG. 33. The trailer length, l_(T), isshown and the transmitter 1280 is located at the end of the trailer 110.The trailer length, l_(T), corresponds to C in the law of cosines. Thedistance, d, between the transmitter 1280 and the receiver 1270 isshown, which corresponds to A in the law of cosines. The referencedistance, d_(r), is a known distance that may be stored in memory 1274.The trailer length, l_(T), may also be a known distance that is storedin memory 1274 or it may be estimated or calculated as described laterherein. The distance, d, is calculated as described hereinafter withreference to FIG. 34.

Referring to FIG. 34, a flow chart of the method 1282 for estimating ahitch angle in accordance with the disclosed subject matter is shown.The method 1282 can be carried out using the vehicle and trailerarchitecture discussed above in reference to the vehicle 100 and trailer110 for FIG. 32. Accordingly the hitch angle estimate may be supplied toany vehicle system 1281 requesting the information.

An operation 1284 is performed for requesting hitch angle estimation. Arequest for hitch angle estimation may come from a vehicle controlsystem 1281 that requires the information as an input to the controlalgorithm associated therewith or it may come from a control system 1281that wants to validate or verify a hitch angle provided by a hitch anglesensor. Examples of vehicle control systems 1281 that may request hitchangle information may be a trailer backup assist system 105, a trailersway control system, a trailer brake control system, and a vehicledynamic control system such as roll stability control or yaw stabilitycontrol. These are only a few examples of systems 1281 that may utilizehitch angle information as an input to a control algorithm.

An operation 1286 is performed to monitor power returns of signalstransmitted from the trailer 110 to the vehicle 100. Path loss isproportional to the square of the distance between the transmitter andthe receiver and power returns of signals transmitted may be used toestimate a distance between the transmitter and the receiver. The powerreturns are measured, at the receiver, at predetermined time intervalsand stored in controller memory over a predetermined period of time. Thepower returns may be accessed by the controller for various operationsand/or functions that use the values to estimate hitch angle.

An operation 1288 is performed to estimate the distance, d, between thetransmitter and the receiver. Estimating the distance, d, between thewireless transmitter and the wireless receiver 1270 is accomplished byusing the, measured power returns or measured path loss of the signalbeing transmitted. Path loss is proportional to the square of thedistance between the transmitter and the receiver, and also to thesquare of the frequency of the transmitted signal. Signal propagationmay be represented by Friis transmission formula:

${P_{r}(d)} = \frac{P_{t}G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}d^{2}L}$

where,

P_(t) is the transmission power in Watts,

G_(t) and G_(r) are gains associated with the receiver and thetransmitter respectively,

λ is the wavelength,

L are system losses, and

d is the distance between the transmitter and the receiver.

Accordingly, transmission power decreases at a rate proportional to d².Therefore, knowing the path loss, PL, associated with the transmittedsignal will provide an estimate of the distance, d, between thetransmitter and the receiver. Path loss (PL) is represented by thefollowing equations:

${PL}_{d\; B} = {{10\; \log \; \frac{P_{t}}{P_{r\;}}} = {{- 10}{\log( \frac{G_{t}G_{r}\lambda^{2}}{4\pi^{2}d^{2}L} )}}}$${PL}_{d\; B} = {{{- 10}{\log( \frac{G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}L} )}} + {10\log \; ( d^{2} )}}$${PL}_{d\; B} = {{{- 10}{\log( \frac{G_{t}G_{r}\lambda^{2}}{( {4\pi} )^{2}L} )}} + {20{\log (d)}}}$

P_(r) decreases at a rate that is proportional to d². The power of thesignal received at the receiver may be represented as:

${P_{r\;}(d)} = {{{P_{r}( d_{0} )}( \frac{d_{0}}{d} )^{2}\mspace{14mu} {for}\mspace{14mu} d} > d_{0} > d_{f}}$

The distance, d, may be derived from this formula and represents theoverall distance between the transmitter on the trailer and the receiveron the vehicle. The distance, d₀, is a known received power referencepoint and the distance, d_(f), is a far-field distance.

The reference distance, d_(r), is known. If the trailer length, l_(T) isknown, then an operation 1289, using the distance, d, the trailerlength, l_(T), the known reference distance, d_(r), between the receiverand the trailer hitch, and the law of cosines, is performed to calculatethe hitch angle. From the law of cosines, provided above, the hitchangle is given by:

$a = {\cos^{- 1}\lbrack \frac{A^{2} - B^{2} - C^{2}}{{- 2}{BC}} \rbrack}$

An operation 1290 is performed in which the vehicle system that isrequesting the information receives the hitch angle estimation. Thedisclosed subject matter provides an estimate of hitch angle even when ahitch angle sensor is unavailable. If a system relies on a hitch anglesensor, the disclosed subject matter may provide verification, as aredundant sensor, that the hitch angle sensor is operating properly.

As discussed above, the trailer length, l_(T), may be a known valuestored in memory or it may be a value that is calculated according tothe disclosed subject matter. The trailer length may be calculated 1292by comparing distances, d, between the transmitter and the receiver thathave been estimated and stored in memory over a period of time. Apredetermined number of distance estimates may be stored in controllermemory. A comparison of the stored distances may result in a largestdistance may be identified. The largest distance estimate may beassociated with a zero hitch angle. This identified largest distance,less the known reference distance, d_(r) will be representative of, andmay be stored as, the trailer length, l_(T).

As an alternative, the trailer length, l_(T), may be estimated using ayaw rate provided by a yaw rate sensor on the vehicle to determine whenthe trailer is a zero hitch angle. A yaw rate sensor is typicallyavailable as part of the sensor system 1200 on the vehicle. A zero yawrate is an indicator that a vehicle is travelling along a straight path,i.e., the vehicle is not turning. The fact that the yaw rate is zeroalone is not adequate to identify a zero hitch angle because the vehiclemay have just stopped turning even though a non-zero hitch angle exists.However, monitoring yaw rate over time will provide confirmation thatthe vehicle has driven straight forward for a sufficient predeterminedperiod of time while maintaining a zero or near zero yaw rate. A zeroyaw rate, sensed over time, provides an indication that the trailer hasstraightened out and it can be inferred that the hitch angle is zero atthat point. Upon verification of zero hitch angle, the operation tocalculate trailer length 1292 is performed. The estimated distancebetween the transmitter and the receiver when the hitch angle is zeroless the predetermined distance, d_(r), defines the trailer length,l_(T).

The predetermined period of time that the yaw rate should remain at zerobefore the assumption that the hitch angle is zero will be associatedwith an actual distance the vehicle trailer combination needs to travelto ensure that the hitch angle is zero. This may be determined throughtesting and stored in the controller memory.

The disclosed subject matter is advantageous in that it provides anestimate of hitch angle whether or not a hitch angle sensor is presenton a vehicle. The disclosed subject matter is even advantageous for avehicle that has a hitch angle sensor in that it provides a method forverifying, or validating, the accuracy of a hitch angle sensed by ahitch angle sensor. This is especially important for vehicle systemsthat rely critically on the value of the hitch angle being sensed, forexample, trailer backup assist systems, trailer sway control systems andtrailer brake control systems.

Hitch Angle Calibration

As previously mentioned with reference to FIG. 10 and a driver'sinteraction with the human machine interface (HMI) device 102, after thetrailer setup module 600 is complete at step 620, the calibration module700, according to one embodiment, calibrates the curvature controlalgorithm with the proper trailer measurements and calibrates thetrailer backup assist system for any hitch angle offset that may bepresent. In the one embodiment, the calibration module 700 may instructthe driver to pull the vehicle-trailer combination straightforward untila hitch angle sensor calibration is complete, which may be notified tothe driver via the HMI device 102. Depending on any error resulting fromthe trailer measurements or the potential inability of the vehicle to bepulled straight forward, additional and alternative embodiments ofcalibrating the trailer backup assist system are described herein.

With reference to FIG. 35, the vehicle trailer backup assist system 105is illustrated having the trailer backup assist control module 120 incommunication with the sensor system 1200 and the trailer backupsteering input apparatus 125 as part of the trailer backup assist system105. The trailer backup assist system 105 in the illustrated embodiment,receives sensor information from the one or more hitch angle sensors1312, a vehicle yaw rate sensor 1314, and a vehicle speed sensor 1316,and may communicate with other conceivable sensors on the vehicle 100 ortrailer 110. For instance, the illustrated embodiment of the trailerbackup assist system 105 also communicates with the vehicle transmissioncontroller 1318, such as receiving the presently engaged transmissiongear. Furthermore, the trailer backup assist control module 120 is alsoin direct communication with the power steering assist system 115, whichhas the power steering assist control module 135 for communicating withthe steering angle detection apparatus 140 and a servo steering motor1300, or servomotor, for operating the steered wheels 1302 of the towingvehicle 100 (FIG. 36). The illustrated embodiment of the trailer backupassist control module 120 includes a microprocessor 1304 for processingone or more routines stored in the corresponding memory 1306 of thetrailer backup assist control module 120. The memory in one embodimentincludes a hitch angle calibration routine 1308 and an initiatingroutine 1310. It should be appreciated that the trailer backup assistcontrol module 120 may be a standalone dedicated controller or may be ashared controller integrated with other control functions, such asintegrated with the sensor system 1200, the trailer backup steeringinput apparatus 125, or other systems of the towing vehicle.

As shown in FIG. 36, a schematic illustration of the vehicle 100 andtrailer 110 combination are overlaid with an x-y coordinate systemshowing kinematic variables and angles, including the steering angle δ,trailer length D, and hitch angle γ, which may be affected by thedynamics of the vehicle 100 and trailer 110 combination andrepresentable in kinematic equations, as similarly discussed withreference to FIG. 5.

Referring to FIGS. 37-38, a method is shown for estimating the actualhitch angle γ(a) between the vehicle 100 and the trailer 110, accordingto one embodiment. The method provides for sensing a measured hitchangle γ(m) with at least one hitch angle sensor 1312 (FIG. 35) on thevehicle 100 and sensing a steering angle δ of the steered wheels 1302(FIG. 36) of the vehicle 100. Further, the method provides for reversingthe vehicle 100, and thereby determining an offset γ(o) between themeasured hitch angle γ(m) and the actual hitch angle γ(a) when themeasured hitch angle γ(m) and the steering angle δ are substantiallyconstant while the vehicle 100 is reversing.

As reflected in the diagram shown in FIG. 36, when the hitch angle γ andsteering angle δ are substantially constant, the yaw rate of the vehicle100 is also substantially constant and equal to the yaw rate of thetrailer 110. This interaction is used to formulate kinematic equationsthat can be solved for determining the offset γ(o) between the measuredhitch angle γ(m) and the actual hitch angle γ(a). Specifically, the yawrate of the vehicle 100, as measured by the vehicle yaw rate sensor 1314(FIG. 35) or another conceivable onboard vehicle sensor that may beconfigured to sense the yaw rate, provides the following equation:

$\frac{\alpha}{t} = {{- \frac{v}{W}}\tan \; \delta}$

Furthermore, the yaw rate of the trailer can be represented with thefollowing equation:

$\frac{\beta}{t} = {{\frac{v}{D}\sin \; \gamma} + {\frac{Lv}{DW}\cos \; {\gamma tan}\; \delta}}$

Where,

δ is the steering angle of the front wheels

D is the distance from the hitch to the trailer axle

W is the vehicle wheelbase (distance between both axles)

L is the distance from the vehicle rear axle and hitch

γ is the hitch angle

Accordingly, when the yaw rate of the vehicle 100 and the trailer 110become equal, the actual hitch angle γ(a) will likely be constant, suchthat the desired hitch angle provided by the trail backup steering inputapparatus 125, such as the previously described rotatable input controldevice shown in FIG. 2, is also constant and substantially achieved. Forexample, the desired hitch angle received from the trailer backupsteering input apparatus 125 may be constant when the driver attempts toreverse the trailer 110 in a straight line with the vehicle 100 (i.e. azero curvature command) or when the driver inputs a maximum knob anglecommand. The resulting constant hitch angle results in the followingequation:

c=a cos γ+b sin γ

This equation can be rewritten as follows:

c=a√{square root over (1−sin²γ)}+b sin γ

The above equation can be solved with the quadratic equation that solvesfor the hitch angle γ. Thereafter, when breaking up the hitch angle γinto a measured hitch angle γ(m) and an offset angle γ(o), the equationcan be rewritten as follows:

$\gamma_{o} = {{\arcsin \; \frac{{bc} \pm {a\sqrt{b^{2} + a^{2} - c^{2\;}}}}{b^{2} + a^{2}}} - \gamma_{m}}$${Where},{c = {{- \frac{1}{W}}\tan \; \delta}}$ $b = \frac{1}{D}$$a = {\frac{L}{DW}\tan \; \delta}$

Accordingly, the hitch angle offset γ(o) may be determined as a functionof the length D of the trailer 110, the wheelbase length W of thevehicle 100, and the distance L from a rear axle of the vehicle 100 tothe trailer 110 as shown in FIG. 36, while meeting the conditionsprovided above to use such an equation. Specifically, the conditionsgenerally include that the vehicle 100 and trailer 110 are reversing andthat the measured hitch angle γ(m) and the steering angle δ aresubstantially constant during the reversing motion for at least athreshold period of time or over a threshold distance of motion.

As illustrated in FIG. 37, the calibration module 700 processes oneembodiment of the hitch angle calibration routine 1308 to provide themethod according to the following steps. At step 1320, the systemreceives generally fixed characteristics of the vehicle 100 and thetrailer 110, including the trailer length D, the vehicle wheelbaselength W, and the distance L from the vehicle's rear axle to the hitchconnection. These generally fixed characteristics are described as suchbecause the vehicle 100 and trailer 110 dimensions can be preloaded orlooked up in product specifications, and if these dimensions are notknown or otherwise already determined by the system, they can bemeasured and input into the memory 1306 or other vehicle memory prior tooperating the vehicle 100 with the trailer backup assist system 105. Thehitch angle calibration routine 1308 shown in FIG. 37, also provides atstep 1322, confirming that the vehicle 100 is reversing when the sensorsof the sensor system 1200 are taking continuous measurements of thevehicle 100 and trailer 110 variables. Specifically, the system mayconfirm that the vehicle 100 is reversing with use of directional speedsensors, the gear position of the transmission controller 1318, GPSinputs, or other conceivable indicators of vehicle 100 direction.

At step 1324, the system conducts the initiating routine 1310 to furtherconfirm that the vehicle 100 and trailer 110 combination are in acondition to determine the offset γ(o) between the measured hitch angleγ(m) and the actual hitch angle γ(a). As shown in FIG. 38, oneembodiment of the initiating routine 1310 includes determining acompensated steering wheel angle 1326, calculating a filtered steeringwheel angle rate 1328, and then determining at step 1330 whether thefiltered steering wheel angle rate is less than a maximum allowablesteering angle rate for the offset calculation. Also, the initiatingroutine 1310 takes the measured trailer angle γ(m) at step 1332 andcalculates a filtered trailer angle rate over time at step 1334. Theinitiating routine then at step 1336 determines whether the filteredtrailer angle rate is less than a maximum allowable trailer angle ratefor determining the offset calculation. Further, the initiating routine1310 takes the sensed or otherwise calculated vehicle speed from step1338 and further calculates a filtered vehicle speed at step 1340. Thefiltered vehicle speed is then processed at step 1342 to determinewhether it is less than a maximum allowable vehicle speed fordetermining the offset calculation. If the conditions of the initiatingroutine 1310 are met at step 1344, the trailer backup assist system 105allows the hitch angle calibration routine 1308 to continue towardsdetermining the offset γ(o).

With further reference to FIG. 37, when the initiating routine 1310 iscomplete, the hitch angle calibration routine at step 1346 determineswhether the hitch angle rate and the steering angle rate are bothsubstantially zero, or alternatively stated, whether the hitch angle andthe steering angles are substantially constant. If the hitch angle rateand the steering angle rate are both not substantially zero, the hitchangle calibration routine 1308 continues to conduct the initiatingroutine 1310 at step 1324 and continues to take measurements with thesensor system 1200 until the hitch angle rate and steering angle rateare substantially zero. Once they are both substantially zero, the hitchangle calibration routine 1308 then determines the actual hitch angle atstep 1348 based on the vehicle 100 and trailer 110 generally fixedcharacteristics, as identified in the equations above. With the actualhitch angle γ(a), the hitch angle calibration routine 1308 may thendetermine the offset γ(o) between the actual hitch angle γ(a) and themeasured hitch angle γ(m) at step 1350. Upon determination of the offsetγ(o), the calibration module is complete and the trailer backup assistsystem 105 may proceed for operation.

In an additional embodiment of the hitch angle calibration routine 1308,as illustrated in FIG. 39, a method is provided for calibrating thetrailer backup assist system 105 for the trailer 110 attached to thevehicle 100, which provides driving the vehicle 100 forwardsubstantially straight above a threshold speed. The method also providessensing a yaw rate of the vehicle 100 and sensing a measured hitch angleγ(m) of the trailer 110. Further, the method provides for determining anangle rate based on the measured hitch angle γ(m), and then determiningan offset γ(o) between the measured hitch angle γ(m) and the actualhitch angle γ(a) when the yaw rate and the angle rate are substantiallyzero.

In the previously described embodiment of the hitch angle calibrationroutine 1308 with reference to FIG. 37, the vehicle 100 is reversing andtherefore such an embodiment is configured for situations when thevehicle 100 may not be able to drive forward far enough to calibrate thetrailer backup assist system 105. However, when space is available todrive the vehicle 100 forward, an alternative method may be used todetermine the offset γ(o) between the actual hitch angle γ(a) and themeasured hitch angle γ(m) that does not rely upon the accuracy of themeasured or otherwise determined trailer geometry and dimensions.Specifically, when setting up the trailer 110 with the vehicle 100, inone embodiment, the user may be instructed to measure various dimensionsof the trailer 110, including the trailer length D. The dimensions ofthe vehicle 100, however, may be measured with a high degree of accuracyupon assembly of the vehicle or otherwise supplied in an accurate mannerto the trailer backup assist system 105, such as with a hookup tableprovided by the vehicle manufacture.

With reference to FIG. 39, at step 700 the trailer backup assist system105 again begins to calibrate the system for the trailer 110 attached tothe vehicle 100. At step 1352, the system receives the vehiclecharacteristic including the dimensions of the vehicle 100 and theoperating characteristics, such as the present gear of the transmission.Then at step 1354, the system confirms that the vehicle is drivingforward while the sensors of the sensor system 1200 take measurementsand other readings. Notably, in this illustrated embodiment, the sensorsutilized include a sensor for determining the vehicle yaw rate, such asan onboard yaw rate sensor 1314 or a separate sensor configured todetermine the yaw rate of the vehicle. Also, the sensors being utilizedby this embodiment of the hitch angle calibration routine include atleast one hitch angle sensor 1312, as previously described withreference to the sensor system 1200.

Still referring to FIG. 39, at step 1356, the steered wheels 1302 of thevehicle 100 are steered straight while the vehicle 100 is travelingforward. It is contemplated that in one embodiment the user may beinstructed to steer the vehicle straight by manually controlling thesteering wheel. In an additional embodiment, the vehicle 100 mayautomatically steer the vehicle 100 straight using the powering steeringassist system 115. More specifically, the trailer backup assist system105 may operate the steered wheels 1302 of the vehicle 100 using theservo steering motor 1300 in conjunction with the steering angledetection apparatus 140.

Once the sensor readings are being received and the vehicle is beingsteered straight and driving forward, the illustrated embodiment of thehitch angle calibration routine 1308 then proceeds to process aninitiating routine 1310 at step 1358. The initiating routine 1310 of thepresent embodiment may, similar to the initiating routine illustrated inFIG. 38, calculate filtered values for the steering wheel angle rate,the hitch angle rate, and the vehicle speed. Furthermore, these filteredvalues may be compared against threshold values to ensure the hitchangle calibration routine is preformed when vehicle conditions areacceptable for such calculation. Specifically, the filtered steeringangle rate may be less than a maximum allowable steering angle rate, thetrailer angle rate may be less than the maximum allowable trailer anglerate, and the filtered vehicle speed may be less than the maximumallowable vehicle speed, such as 10 mph, 15 mph, or other conceivablethreshold speed. When these or more or fewer conditions are met, thesystem may proceed to the following step of the hitch angle calibrationroutine.

As also illustrated in FIG. 39, at step 1360 the hitch angle calibrationroutine 1308 determines whether the hitch angle rate and the yaw rateare both substantially zero. Specifically, the determination of reachinga value of substantially zero may be one or a combination of the valuebeing within a close proximity to zero or the value being zero orsubstantially zero over a predetermined period of time. It iscontemplated that the increment of time may be proportional to thefiltered vehicle speed, such that increasing speed of the vehicleresults in decreasing the increment of time the measured hitch angleγ(m) and the steering angle must be substantially constant to determinethe offset γ(o). It is also contemplated that the offset may bedetermined when the measured hitch angle and the steering angle aresubstantially constant while the vehicle and the trailer are reversingover a threshold distance, such as a distance is greater than half acircumference of a steered wheel of the vehicle or other conceivabledistances. When the system makes a determination that both values aresubstantially zero, the system, at step 1362 is then able to determinethe actual hitch angle γ(a) based upon the vehicle characteristics. Inone embodiment, when the above conditions are met the actual hitch angleγ(a) will be zero. However, some vehicle characteristics, such as anoffset hitch location, may result in the actual hitch angle γ(a)deviating from zero with these conditions met. At step 1364 the systemthen determines the offset γ(o) between the actual hitch angle γ(a) andthe measured hitch angle γ(m) for purposes of operating the trailerbackup assist system 105. Again, at step 704 the trailer backup assistsystem 105 may notify the driver that the calibration is complete andmay store the hitch angle offset value in memory to be associated withthe attached trailer 110.

Referring now to FIG. 40, an additional embodiment of the hitch anglecalibration routine 1308 is illustrated that may consider the vehicle'sdirection of movement or potential direction of movement before choosinga method for determining the offset γ(o) of the measured hitch angleγ(m). The vehicle's direction of movement may be based upon thepresently engaged gear of the transmission, such as drive or reverse forautomatic transmissions. The vehicle's potential direction of movement,however, may be based upon the available space in front of or behind thevehicle and trailer combination. At step 1366, if the vehicle 100 ismoving in either the forward or rearward directions, the system maydetermine if enough available space exists for the vehicle 100 tocontinue moving in such direction and complete the calibration of thetrailer backup assist system 105. If enough available space is notpresent, the hitch angle calibration routine 1308 of the illustratedembodiment may instruct the driver to move the vehicle 100 in theopposite or an alternative direction, provided enough available spaceexists in such direction to complete the calibration. Also, if thevehicle 100 is not moving, the system may determine the preferreddirection of movement for the vehicle 100 and trailer 110 to move tohave enough space for the vehicle 100 to complete the calibration of thetrailer backup assist system 105. At step 1368 the system may instructthe driver, such as through the HMI, to drive either forward or inreverse, as determined in the previous step 1366. Based on whichdirection the vehicle is instructed to move, this embodiment of thehitch angle calibration routine 1308 may employ one of two alternativemethods to determine the actual hitch angle γ(a) for completing thecalibration. Specifically, if the vehicle 100 is traveling forward, atstep 1370, the system then proceeds to ensure that the vehicle issteered straight 1372, while sensing the yaw rate of the vehicle 1374and sensing the hitch angle rate 1376. The sensed hitch angle γ(m) isused by the system to determine the hitch angle rate at step 1378 andthen continue on to step 1380 to determine when the hitch angle rate andthe yaw rate of the vehicle are substantially zero, similar to themethod previously described with reference to the embodiment disclosedin FIG. 39. When the hitch angle rate and the yaw rate of the vehicleare substantially zero, at step 1380 the hitch angle calibration 1308routine may determine the actual hitch angle γ(a) to be substantiallyzero, which may then be used in conjunction with the measured hitchangle γ(m) to determine the offset γ(o) at step 1382.

Alternatively, if the vehicle 100 is reversing or instructed to reverse,at step 1384, once the vehicle 100 is reversing, the system proceeds tosense the steering angle δ of the vehicle 100 at step 1386 and sense thehitch angle γ(m) at step 1388 to then determine the hitch angle rate andthe steering angle rate at step 1390. At step 1392 the system determineswhen both the hitch angle rate and the steering angle rate aresubstantially zero. When both these values are substantially zero, thehitch angle calibration routine 1308 may determine the offset γ(o) ofthe measured hitch angle γ(m) based upon the length D of the trailer110, the wheelbase length W of the vehicle 100, and the distance L fromthe rear axle of the vehicle 100 to the trailer 110, as generally setforth in the embodiment of the hitch angle calibration routine 1308described with reference to FIGS. 37 and 38. In the embodiment disclosedin FIG. 40, once the hitch angle offset γ(o) is determined at step 1382,the calibration routine commences at step 704 and may notify the driver,such as via the HMI or another similar notification.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

What is claimed is:
 1. A method of estimating an actual hitch anglebetween a vehicle and a trailer, comprising: sensing a measured hitchangle with a hitch sensor on the vehicle; sensing a steering angle ofsteered wheels of the vehicle; reversing the vehicle; and determining anoffset between the measured hitch angle and the actual hitch angle whenthe measured hitch angle and the steering angle are substantiallyconstant while the vehicle is reversing.
 2. The method of claim 1,wherein the offset is determined as a function of a length of thetrailer, a wheelbase length of the vehicle, and a distance from a rearaxle of the vehicle to the trailer.
 3. The method of claim 1, furthercomprising: steering the reversing vehicle with a servomotor to move thevehicle and the trailer from the actual hitch angle to a desired hitchangle.
 4. The method of claim 3, further comprising: selecting thedesired hitch angle between the vehicle and the trailer with a rotatableinput control device and steering the vehicle in reverse based on themeasured hitch angle, the offset, and the desired hitch angle.
 5. Themethod of claim 1, further comprising: selecting a desired hitch anglehaving zero curvature; and steering the reversing vehicle based on theoffset to position the vehicle and the trailer together in a straightline.
 6. The method of claim 1, wherein the hitch sensor includes avideo imaging camera that monitors a target on the trailer forcontinuously sensing the measured hitch angle.
 7. The method of claim 1,wherein the offset is determined when the vehicle maintains a speedgreater than a threshold speed for an increment of time.
 8. A method ofestimating an actual hitch angle between a vehicle and a trailer,comprising: sensing a measured hitch angle continuously; sensing asteering angle of the vehicle continuously; determining an offsetbetween the measured hitch angle and the actual hitch angle when themeasured hitch angle and the steering angle are substantially constantwhile the vehicle and the trailer are reversing over a thresholddistance.
 9. The method of claim 8, wherein the vehicle reverses overthe threshold distance when the vehicle maintains a speed greater than athreshold speed for an increment of time.
 10. The method of claim 9,wherein the increment of time is proportional to the speed, such thatincreasing the speed of the vehicle results in decreasing the incrementof time the measured hitch angle and the steering angle must besubstantially constant to determine the offset.
 11. The method of claim8, further comprising: providing a length of the trailer, a wheelbaselength of the vehicle, and a distance from a rear axle of the vehicle tothe trailer, wherein the offset is determined by a controller based onthe length of the trailer, the wheelbase length of the vehicle, and thedistance from a rear axle of the vehicle to the trailer.
 12. The methodof claim 8, wherein the threshold distance is greater than half acircumference of a steered wheel of the vehicle.
 13. The method of claim8, further comprising: steering the reversing vehicle based on theoffset to move the vehicle and the trailer from the measured hitch angleto a desired hitch angle.
 14. The method of claim 13, furthercomprising: rotating an input control device to select the desired hitchangle between the vehicle and the trailer.
 15. The method of claim 8,further comprising: selecting a desired hitch angle having asubstantially zero curvature; and steering the reversing vehicle basedon the offset to position the vehicle and the trailer together in astraight line.
 16. The method of claim 8, wherein the measured hitchangle is continuously sensed with a hitch sensor that includes a videoimaging camera that monitors movement of a target on the trailer.
 17. Asystem for estimating an actual hitch angle between a vehicle and atrailer, comprising: a hitch sensor on the vehicle continuously sensinga measured hitch angle; a steering sensor continuously sensing asteering angle of the vehicle; and a controller determining an offsetbetween the measured hitch angle and the actual hitch angle when themeasured hitch angle and the steering angle are substantially constantwhile the vehicle and the trailer are reversing.
 18. The system of claim17, wherein the offset is determined as a function of a length of thetrailer, a wheelbase length of the vehicle, and a distance from a rearaxle of the vehicle to the trailer.
 19. The system of claim 18, whereinthe offset is determined when the vehicle and the trailer each maintaina substantially constant yaw rate.
 20. The system of claim 18, whereinthe offset is determined when the vehicle and the trailer reverse over athreshold distance while maintaining the measured hitch angle and thesteering angle at substantially constant values.